When developing Dokku, it is useful to use a real domain to test actual functionality. This is impossible if the domain is hardcoded to dokku.me in testing.
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
The URLS file is no longer necessary as urls are now generated directly from the app VHOST file.
This also moves all the url generation logic to the domains plugin.
This makes the installation a bit more secure by ensuring a user does not accidentally expose a way for unauthorized users to add new ssh keys to the system.
Additionally, this removes the extra HOSTNAME file to make the initial install process easier (that file was not modifiable by any dokku commands.
Closes#2247
