Add a way to preview/render the final generated commit message locally

[jraygauthier]

Tell us more.

I would like to propose adding a way to inspect the final rendered commit
message without having to run Renovate against a real platform and create a
branch/PR.

Currently, --print-config shows the templates, for example:

{
  "commitMessage": "{{{commitMessagePrefix}}} {{{commitMessageAction}}} {{{commitMessageTopic}}} {{{commitMessageExtra}}} {{{commitMessageSuffix}}}"
}

However, it does not show the final rendered commit message after applying:

• dependency context (depName, currentVersion, newVersion, etc.)
• semantic commit handling
• grouping
• casing rules

For example, when customizing Conventional Commit output, it would be useful
to preview:

build(go-mod.lmittmann-tint): 1.1.0 -> 1.2.0

without requiring a real Bitbucket/GitHub/etc. run.

A possible solution could be:

• make --dry-run print the final generated commit message;
• add a dedicated command/option to render a commit message from an update
  context.

For example:

renovate --render-commit-message ...

I found PR #9014, which appears related to improving visibility around commit
message generation, but it is unclear why it was closed and whether the
functionality was superseded.

Would maintainers consider exposing the final rendered commit message during
dry runs, or providing a local rendering command?