Hold all PRs in stable repo for prometheus* charts

[scottrigby]

Existing prometheus PRs in stable are on hold for now (see linked PRs on prometheus-community/community#28), but we don't have any automated way to hold new PRs that may open between now and when that issue is resolved (this new helm repo ready to be transferred to prometheus-community, stable prometheus charts deprecated, new helm repo with charts listed on the hubs).

Maintainers: Please help with this if you see new PRs for prometheus charts open in the meantime.

Let's keep this open to track the effort, until the above is complete.

• Existing prometheus PRs in stable
• New prometheus PRs in stable

[scottrigby]

I did another round of this last night

[scottrigby]

Myself and a few others have been doing this all along.

Now that #28 is finished, and we've been keeping up with this issue along the way, we can close this now and move onto #29