Add recommendations about gitignore usage

Background

As discussed in apertis-infrastructure!223 (merged) it is useful to have clear guidelines on how to use gitignore, and other configurations to follow the same rules across repositories.

Outcomes

TBD

Management data

This section is for management only, it should be the last one in the description.

/cc @em @Balasubramanian @sudarshan @wlozano

Phabricator link: https://phabricator.apertis.org/T10830