Support for per-component Release-As commit comment

[Cavaler]

Currently adding "Release-As" comment body forces that version on all released components.
Ability to specify a component in the commit body would be welcome, something like "component-name-Release-As".

I know that you can specify it in the release-please-config.json as well, but that requires adding a line there, making a release, and then making another commit removing that line, which probably can trigger another root release...