repo_management/convert.py:
Add the class `RepoDbFile` which is used to initialize a jinja
environment and allows to render the 'desc.j2' and 'files.j2' templates.
Add `_desc_data_line_to_dicts()` which allows for assigning the data
from a line in a 'desc' file to be assigned to a dict, that corresponds
to the line's designated data type.
Simplify `_desc_data_to_model()` by making use of
`_desc_data_line_to_dicts()`.
Change `_desc_data_to_model()` by guarding against pydantic
ValidationErrors and raising a RepoManagementValidationError instead.

tests/test_convert.py:
Add tests for `RepoDbFile`.