Support JSON Change Log for Strategies

Thanks for stopping by to let us know something could be better!

**Is your feature request related to a problem? Please describe.**

As part of automating tracking of changes in releases and updating our JIRA ticketing system, it would be helpful if the Change Log was generated in machine readable format (for example JSON).

However, currently release please, only supports [ChangelogJson](https://github.com/googleapis/release-please/blob/main/src/updaters/changelog-json.ts) for a limited number of strategies (node; python; java-yoshi-mono-repo).

**Describe the solution you'd like**

Update the [base strategy](https://github.com/googleapis/release-please/blob/main/src/strategies/base.ts) so that it optionally supports generation of [ChangelogJson](https://github.com/googleapis/release-please/blob/main/src/updaters/changelog-json.ts) for all strategies.

**Describe alternatives you've considered**

Attempting to manually process the Markdown change log and / or manually extracting the conventional commit messages from git history - however, getting this from a file generated by Release Please would be more elegant and reduce repetition.

**Additional context**

None