Adds an app-aware `fn-verify-app-image` helper that pulls the deployed image
from the configured registry when it is missing locally, gated on
push-on-release being enabled, honoring per-app `registry:login` credentials.
Every in-tree `verify_image` caller migrates to the wrapper and the bare
helper is marked deprecated. `config:set` now forwards the deployed image tag
to `release-and-deploy` so the release path no longer pins recovery on the
unrecoverable `:latest` tag.
Building/testing for ARM does not happen often - the only runtime environment is Raspberry PI, which supports ARM64 - and complicates support for a ton of features. Aside from that, CI runs are much longer for ARM Dokku images, often reaching 15-20 minutes or just timing out completely.
Rather than support an architecture that doesn't have much usage by maintainers and has a lot of maintenance burden, we're removing the platform.
We will not provide support for herokuish on either as herokuish is meant to be Heroku-compatible, and the Heroku stack does not support arm. Use 'pack' or Dockerfiles for app building instead.
We don't skip pack as in theory they may be able to support arm in the future. Dockerfile builds should work fine, as long as all images in the FROM directives have arm versions.
Finally, the null builder _should_ always work, but of course YMMV :D
This standardization makes it somewhat easier to read stacktraces as the command names are all uniform, so it will be slightly easier to scan trace output.
This PR uses the new syntax for commands introduced in Docker 1.13, making it a bit easier to understand just what a particular command is trying to do.
This also pushes the long-form syntax for docker command flags, which are also easier to understand at a glance.
This reduces duplication and allows users to rely on global arguments to generate most labels needed.
The 'commit' command cannot have global arguments because the whitespace within the label change breaks string-based interpolation, and shell arrays cannot be exported.
This change allows operators to specify a DOCKER_BIN environment variable. This will specify a binary to run when executing docker, which is useful in cases where the 'docker' command being run must be modified in a way that would otherwise be invasive to Dokku, but minimalistic if done within a wrapper.
While I do not agree with _every_ style change, this will force Dokku to have consistent formatting across all shell scripts, which is arguably a Good Thing™.
The command used to reprocess everything is:
```shell
shfmt -l -bn -ci -i 2 -w .
```
This allows users to quickly show the state of any configured application, as well as the state of their server. In doing so, we make it easy for them to provide information necessary for debugging in a single command.
