support edit_uri_template by using at least mkdocs >=1.4.0

Release https://github.com/mkdocs/mkdocs/releases/tag/1.4.0
introduces a new feature edit_uri_template
which is a more flexible version of edit_uri.

I've prepared changes to utilize this at
https://github.com/backstage/backstage.

Note:
mkdocs v1.4.2 supports Python 3.11
https://github.com/mkdocs/mkdocs/releases/tag/1.4.2

Related: https://github.com/backstage/mkdocs-techdocs-core/issues/107

No file or test is named. Start by reviewing the current handling of edit_uri and the project's MkDocs dependency, then compare it with MkDocs 1.4.0's edit_uri_template behavior; done means the plugin supports the template while preserving existing edit_uri behavior and the Backstage use case.

Written by the indexing model from the issue text.