Optimise project clone for search

As a developer; running a `grep` can be optimized by reducing available files in the repository. We could rely on git sparse checkout to get only interesting files available per clone.

Hints:

• Check https://git-scm.com/docs/git-sparse-checkout/2.27.0
• Consider sparse checkout definition to be updated over time and not fixed per clone.
• https://github.com/nuxeo/nos/blob/master/docs/tech-decisions/2020-08-Statistic-Extractor.md#git-clone-strategy

AC:

• as a user, I never get a hit on a non-desirable file: like in a minified js lib.