use self-hosted runners for core branches

[lahabana]

Description

We have 2 problems with CI still:

• arm free runners don't exist on github
• the max parallel runners is limited in github free and causes queueing

To alleviate this using self-hosted runners sponsored by Kong would be ideal (it's a setup we use for our enterprise builds). This ticket tracks:

• [x] Bringing up self-hosted runners on hetzner
• [x] Register the self-hosted runners with the kumahq org
• [x] #10583
• [x] https://github.com/kumahq/kuma/issues/10904
• [x] #10585
• [x] #10584

[jijiechen]

As of 15 Aug, self hosted runners are enabled for running E2E tasks on:

ARCH	Branch	Enabled
AMD64	master	Y
AMD64	release-* >= 2.6	N (planned)
ARM64	master	Y
ARM64	release-* >= 2.6	Y

CircleCI code is cleaned up on master and release-* >= 2.6.

[lahabana]

I think we should not bother with AMD64 for release-* >= 2.6 . Let's just focus on having self-hosted runners reliably pass on master.