setup: use importlib instead of pkg_resources

Address warnings like:
UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
import pkg_resources

config: move various py templates to kallithea/templates/py/

For some reason, we had some python templates in kallithea/config .
kallithea.config is mainly the TG entry point, and thus a high level controller
thing - not a place to store templates.

Instead, use the templates directory and introduce a new py subdirectory.

With git hook templates in a templates directory, there is no need for tmpl in
the name.

extensions: rename 'rcextensions' into 'extensions' but provide compatibility

The 'rc' prefix is legacy.
Rename 'rcextensions' into 'extensions', updating all references.
Compatibility with the old name will be retained for a while, and removed in
a later release. Migrating is as simple as renaming a file.

utils2: Move ask_ok out of paster_commands

The ask_ok function is still a mess and should be cleaned up ...

cli: convert 'gearbox make-rcext' in 'kallithea-cli extensions-create'

Note: 'extensions' instead of 'rcextensions' as first step to get away from
the 'rc' prefix.