Previously, we would always set the port mapping during a dockerfile build, making it difficult for users to override mappings. We also only _sometimes_ updated the detected port mapping, further confusing issues when users were migrating from Dockerfile to Buildpacks for builds.
Now, we always detect the port mapping during the build process, and only use that detected port mapping if an override is not specified. This greatly simplifies the experience around port mapping, as now a user can create an app, set a port mapping, and that first deploy will respect the port mapping without an additional deploy.
The builder always has the best context for what the app should be listening on, and thus we can always specify a "default" port mapping at this stage. Users can override this map as desired later.
This change also results in the removal of a ton of internal code that is now centralized in the ports plugin.
Closes#4067
During an app build, we now auto-detect ports based on the source code. This is usually http:80:5000, with Dockerfile-based deploys having their ports extracted from the docker image or Dockerfile. Additionally, we add an https:443 mapping for any detected http:80 mapping when there is an ssl certificate, and all http port mappings are transformed to https mappings for Dockerfile-based deploys.
While the ports aren't currently consumed, a future refactor will provide the ability to fallback to the new detected ports when there is no user-specified port mapping.
We should treat the project.toml as an optional file, as is the Procfile. Additionally, moving the file into place early will ensure there is no chance of selecting the wrong file.
