Support self-hosted Github Actions for integration/e2e testing

[sp-yduck]

/kind feature

Describe the solution you'd like

Current CI is supporting only Unit testing (and linting). as the project is getting bigger, it would be helpful if we can support integration/e2e test in the CI.
Since integration/e2e testing need to work with ProxmoxVE, CI may need to be self-hosted.

Anything else you would like to add:
[Miscellaneous information that will assist in solving the issue.]

Environment:

• Cluster-api-provider-proxmox version:
• Proxmox VE version:
• Kubernetes version: (use kubectl version):
• OS (e.g. from /etc/os-release):

[sp-yduck]

it seems self-hosted runners are not recommended for public repos
https://docs.github.com/en/actions/hosting-your-own-runners/managing-self-hosted-runners/adding-self-hosted-runners

need to consider other way