Add create and update file to RepositoryClient

[dlemaigl]

Add methods to create and update a file.

GitHub API -> https://docs.github.com/en/rest/repos/contents?apiVersion=2022-11-28#create-or-update-file-contents

[ebk45]

Hi @dlemaigl.

We apologise for taking so long to get eyes on this PR, we haven't been able to maintain this library to the standard we would have liked to but this will be changing in the new year. If you could please get this rebased and we'll be prioritising all open PRs ready for review.

Thanks!

Ellie

[felix-seifert]

Hi @dlemaigl,

PR #148 implemented the same functionality (with minor differences). As its branch was recently rebased, we decided to merge it. Therefore, your PR becomes redundant and I will close it.

We sincerely thank you for your contribution, and if some functionality is missing, we welcome every new PR.

Kind regards,
Felix