GitHub sponsors

[Xpirix]

Fix for #551

• Added a new page to list the GitHub sponsors
• Added a new workflow to update the GH sponsors' page using https://github.com/JamesIves/github-sponsors-readme-action
• The workflow will be triggered every day at midnight & noon UTC but can also be triggered manually from the Actions tab.
• The workflow will automatically commit the scrapped data (like the donors scrapping workflow).

NOTE: The current changes were not tested from my side as I don't have any available data to test with. I will submit additional fixes if needed.

[timlinux]

@Xpirix Maybe in that red box area, you can put a call to action like 'be the first GitHub sponsor!' or something?

[Xpirix]

Maybe in that red box area, you can put a call to action like 'be the first GitHub sponsor!' or something?

@timlinux The GH actions workflow will get the existing sponsors from https://github.com/sponsors/qgis once triggered. I see that there are already some sponsors there. Perhaps we could say Want to see your name here? and link it to the GH sponsor page.

[timlinux]

LGTM thanks!