Renames the existing `## Internal properties` umbrella section to `## Properties` across all plugin docs and adds a new `### Settable properties` subsection enumerating every property accepted by each plugin's `:set` command. Each row lists scope, default, the actual `:report` flag shapes that surface the value, and a one-line description. The buildpacks plugin is included even though it uses `:set-property`, with a note in the subsection clarifying the legacy command name. Property lists, scopes, and report flags were verified against plugin source and the live dokku binary.
The `<plugin>-global-<property>` keys in `:report` output returned the resolved value with the built-in default substituted in, so external tooling could not distinguish a property that had been set globally to the default from one that had never been set. The bare keys for caddy, haproxy, and traefik global-only properties had the same shape. The `global-<property>` keys now hold the raw stored value and are empty when nothing has been set, and a new `computed-<property>` key holds the effective value used at runtime, falling back through the per-app value (where one exists), the global value, and the built-in default. The bare global-only keys for the three proxy plugins are removed in favor of the raw/computed pair. Closes#8631.
Per-plugin management docs now describe the properties introduced by the env-var-to-property migration in PR #8498, and stale prose and command-output examples that still referenced the old `DOKKU_*` names have been refreshed. The deprecated env vars table moves out of `environment-variables.md` and into the 0.38.0 migration guide, where it functions as a one-time pointer for upgrading users rather than ongoing reference material.
Exposing all config values will allow users to skip setting environment variables twice - once as a docker option and once as an env var. Docker will automatically pull the value from the environment if none is set for the --build-arg flag.
Users will still be required to specify each desired env var via --build-arg as otherwise docker builds will complain about unused build arguments.
Re-implements #5978 (lost in a rebase)
Closes#5903
Recent Dokku changes invalidate a bunch of docs around where files need to be placed in order for Dokku to respect them. This doc change clarifies where files are extracted from in cases where source code is available, which should hopefully make users less confused about how the system works.
See https://railsnotes.xyz/blog/deploying-ruby-on-rails-with-dokku-redis-sidekiq-arm-docker-hetzner for the inspiration - I was reading through it and was like 'these docs are definitely incorrect...'.
While we will still build for 18.04, we will now stop testing against it. Instead, we will test against 20.04, the next EOL release after 18.04.
Once Ubuntu 18.04 is EOL, any references to it will also be removed.
Note that 18.04 support was already deprecated in Dokku 0.28.0, so this change is just acknowledging that deprecation.
