Multinode workflow: use github user's ssh key

[elelaysh]

changes to stackhpc-multinode.yml:

• new github_user_ssh_keys input (defaults to true)
• previous input ssh_key is still here and overrides github_user_ssh_keys

[gemini-code-assist]

Note

Gemini is unable to generate a review for this pull request due to the file types involved not being currently supported.

[elelaysh]

Multiline input is not supported in github actions, see
this discussion for instance.

So the ssh_key input still only supports a single key. If we want to extend this, we could check if the first character is a square bracket ([) and assume the input is already a json-encoded array in this case.

Should I implement that?

[elelaysh]

Needs stackhpc/stackhpc-openstack-gh-workflows#17

[elelaysh]

thank you