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

I cannot make release-please bump the version string inside any other Python file than __init__.py, as this is today hard-coded:

Some Python projects doesn't use __init__.py to store the version string. Some projects like to place this in a __about__.py file or __version__.py file instead. In short, this separates concerns so that the version string can be watched outside of any other potential code changes. In my case, I wanted release-please to bump an __about__.py file.

Describe the solution you'd like

• I'd like to have release-please attempt to bump __init__.py like it does today for backwards compatibility reasons.
• I'd like to define the desired filename in which the version string will be bumped, using the version-file manifest configuration (but this is currently not taken into consideration for release-please's Python strategy).

Describe alternatives you've considered

N/A

PR proposal

This enables the use of version-file: #2434