Script: New Version

[ax3l]

Adding a script to update all version notes programmatically for releases.

• finish script
• document how to use it in Maintenance section of manual, similar to https://warpx.readthedocs.io/en/latest/maintenance/release.html

[franzpoeschel]

I've adapted this to openPMD now. It's mostly text search and replace, I've entirely removed the dependency and config file management that WarpX uses since it does not really apply to our use cases.
Note that moving this to another directory means that the REPO_DIR definition must be changed too:

REPO_DIR = Path(__file__).parent.absolute()