Review script/entrypoint names

This issue has been migrated from [#12303](https://github.com/matrix-org/synapse/issues/12303).

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Some of them are generic like `generate_config` and `hash_password` and ought to include a `synapse_` prefix or similar. We might consider pruning these if they're not useful too. These are things that eventually end up on people's `PATH`s with no context. We should choose names carefully and respectfully.

We should be able to effect any renames by changing setup.py/pyproject.toml and possibly the debian package config. We shouldn't need to rename any script files within the project. We'll also need to mention this in the upgrading notes.