Add 'contents: write' permissions to docfx build GitHub Action

[MihaZupan]

Grants the GITHUB_TOKEN permissions to push the updated docs to the gh-pages branch.

reverse-proxy/.github/workflows/docfx_build.yml

Lines 46 to 47 in da38760

	git remote set-url origin https://x-access-token:${{ secrets.GITHUB_TOKEN }}@github.com/${{ github.repository }}
	git push origin gh-pages

Guessing contents is the right category based on https://docs.github.com/en/actions/using-jobs/assigning-permissions-to-jobs#:~:text=contents,GitHub%20Apps.%22