Add buildpacks:set --replace so callers can replace an app's complete ordered buildpack list in one command while preserving existing single-buildpack and --index behavior.
Closes#8802
Every Go-implemented plugin's `:report --format json` now emits keys without the redundant `<plugin>-` head segment, matching the shape bash plugins have always emitted. The CLI flag names and `:set` semantics are unchanged. For backwards compatibility during the 0.38.x patch series, the legacy `<plugin>-<property>` keys are emitted side-by-side with the new keys, and a future major release will drop the legacy keys. `common.ReportSingleApp` is refactored to accept a `ReportSingleAppInput` struct with a `Validate()` method so the input is checked before any work runs, which also catches the latent `"docker options"` reportType bug at the API boundary.
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 buildpacks entry in tests/apps/dockerfile/app.json caused
the post-extract trigger to write a .buildpacks file during
Dockerfile-based deploys, breaking builder detection. Remove
the entry and add Go unit tests for getBuildpacks/validBuildpackURL,
a bats integration test for deploying with app.json buildpacks,
and documentation for the new feature.
