replace PathMixin and RepositoryApiMixin

[Panaetius]

To get rid of PathMixin and RepositoryApiMixin move the following properties to the config class from #3081 and use the config dispatcher where they are needed.

• RepositoryApiMixin.renku_home
• RepositoryApiMixin.renku_path
• RepositoryApiMixin.parent
• RepositoryApiMixin.data_dir
• RepositoryApiMixin.docker_path
• RepositoryApiMixin.template_checksums
• RepositoryApiMixin.database_path

In addition, LOCK_SUFFIX, DATABASE_PATH, DOCKERFILE, TEMPLATE_CHECKSUMS, RENKU_PROTECTED_PATHS and DATABASE_METADATA_PATHshould just be module level constants in renku/core/constant.py.

We should remove attrs and replace it with proper __init__.

with_metadata should be a ProjectContext (or similar) context manager.
is_project_set can be removed, as it's only used in one place and essentially useless.
RepositoryApiMixin.project should be removed as well in favor of using the IProjectGateway directly.
transaction_id can probably be moved to Repository.
All the methods should be normal business logic methods, unless they really need to be on a class.

The locks can be added to the lock class from #3082 that also gets injected.

blocked by #3081