feat: add support for nixpacks as a builder

Closes #5338

docs/deployment/builders/nixpacks.md

@@ -0,0 +1,155 @@
+# Nixpacks
+
+> New as of 0.32.0
+
+The `nixpacks` builder builds apps via [Nixpacks](https://nixpacks.com/), a buildpack alternative.
+
+## Usage
+
+### Requirements
+
+The `nixpacks` cli tool is not included by default with Dokku or as a dependency. It must also be installed as shown on [this page](https://nixpacks.com/docs/install#debian-(and-derivatives-like-ubuntu)).
+
+Builds will proceed with the `nixpacks` cli for the app from then on.
+
+### Detection
+
+This builder will be auto-detected in the following case:
+
+- A `nixpacks.toml` exists in the root of the app repository.
+
+The builder may also be selected via the `builder:set` command
+
+```shell
+dokku builder:set node-js-app selected nixpacks
+```
+
+### Supported languages
+
+See the [upstream nixpacks documentation](https://nixpacks.com/docs) for further information on what languages and frameworks are supported.
+
+### Build-time configuration variables
+
+For security reasons - and as per [Docker recommendations](https://github.com/docker/docker/issues/13490) - nixpacks-based deploys have variables available only during runtime.
+
+For users that require customization in the `build` phase, you may use build arguments via the [docker-options plugin](/docs/advanced-usage/docker-options.md). All environment variables set by the `config` plugin are automatically exported within the nixpacks build environment, and thus `--env` only requires setting a key without a value.
+
+```shell
+dokku docker-options:add node-js-app build '--env NODE_ENV'
+```
+
+Alternatively, a full value may be provided in the form of `--env KEY=VALUE`:
+
+```shell
+dokku docker-options:add node-js-app build '--env NODE_ENV=production'
+```
+
+### Changing the `nixpacks.toml` location
+
+When deploying a monorepo, it may be desirable to specify the specific path of the `nixpacks.toml` file to use for a given app. This can be done via the `builder-nixpacks:set` command. If a value is specified and that file does not exist in the app's build directory, then the build will fail.
+
+```shell
+dokku builder-nixpacks:set node-js-app nixpackstoml-path nixpacks2.toml
+```
+
+The default value may be set by passing an empty value for the option:
+
+```shell
+dokku builder-nixpacks:set node-js-app nixpackstoml-path
+```
+
+The `nixpackstoml-path` property can also be set globally. The global default is `nixpacks.toml`, and the global value is used when no app-specific value is set.
+
+```shell
+dokku builder-nixpacks:set --global nixpackstoml-path nixpacks2.toml
+```
+
+The default value may be set by passing an empty value for the option.
+
+```shell
+dokku builder-nixpacks:set --global nixpackstoml-path
+```
+
+### Disabling cache
+
+Cache is enabled by default, but can be disabled by setting the `no-cache` property to `true`:
+
+```shell
+dokku builder-nixpacks:set node-js-app no-cache true
+```
+
+The default value may be set by passing an empty value for the option:
+
+```shell
+dokku builder-nixpacks:set node-js-app no-cache
+```
+
+The `no-cache` property can also be set globally. The global default is `false`, and the global value is used when no app-specific value is set.
+
+```shell
+dokku builder-nixpacks:set --global no-cache true
+```
+
+The default value may be set by passing an empty value for the option.
+
+```shell
+dokku builder-nixpacks:set --global no-cache
+```
+
+### Displaying builder-nixpacks reports for an app
+
+You can get a report about the app's storage status using the `builder-nixpacks:report` command:
+
+```shell
+dokku builder-nixpacks:report
+```
+
+```
+=====> node-js-app builder-nixpacks information
+       Builder-nixpacks computed nixpackstoml path: nixpacks2.toml
+       Builder-nixpacks global nixpackstoml path:   nixpacks.toml
+       Builder-nixpacks nixpackstoml path:          nixpacks2.toml
+       Builder-nixpacks computed no cache:          true
+       Builder-nixpacks global no cache:            false
+       Builder-nixpacks no cache:                   true
+=====> python-sample builder-nixpacks information
+       Builder-nixpacks computed nixpackstoml path: nixpacks.toml
+       Builder-nixpacks global nixpackstoml path:   nixpacks.toml
+       Builder-nixpacks nixpackstoml path:
+       Builder-nixpacks computed no cache:          false
+       Builder-nixpacks global no cache:            false
+       Builder-nixpacks no cache:
+=====> ruby-sample builder-nixpacks information
+       Builder-nixpacks computed nixpackstoml path: nixpacks.toml
+       Builder-nixpacks global nixpackstoml path:   nixpacks.toml
+       Builder-nixpacks nixpackstoml path:
+       Builder-nixpacks computed no cache:          false
+       Builder-nixpacks global no cache:            false
+       Builder-nixpacks no cache:
+```
+
+You can run the command for a specific app also.
+
+```shell
+dokku builder-nixpacks:report node-js-app
+```
+
+```
+=====> node-js-app builder-nixpacks information
+       Builder-nixpacks computed nixpackstoml path: nixpacks2.toml
+       Builder-nixpacks global nixpackstoml path:   nixpacks.toml
+       Builder-nixpacks nixpackstoml path:          nixpacks2.toml
+       Builder-nixpacks computed no cache:          true
+       Builder-nixpacks global no cache:            false
+       Builder-nixpacks no cache:                   true
+```
+
+You can pass flags which will output only the value of the specific information you want. For example:
+
+```shell
+dokku builder-nixpacks:report node-js-app --builder-nixpacks-no-cache
+```
+
+```
+true
+```