Improve join robustness

[martencassel]

This PR will attempt to improve join robustness and handle the cases of

1. We can authentication errors, we perform retries for a number of times until giving up.
2. We handle existing accounts, and optionally from the config, skip touching these accounts.

Handling

#22
#27
#20

[dsnpl]

This looks really good to me and much better than (dsnpl@a18ce9c88e321ad6399b884e87388fcb5ce57a74)[my attempt] -

I found that with multiple DCs requests get sequentially round-robined and that the set password request after the create create object request goes to a different DC that hasnt had the new object synced to it. Retrying for up to about 10 seconds sorts this out for me.

[martencassel]

Ping @ekohl

[ekohl]

This PR does a few things. Would you mind separating it into smaller PR? Preferably start with the CI updates

[ekohl]

For CI we've introduced a common workflow but not app plugins have adopted it. I'd prefer to do that. https://github.com/theforeman/actions?tab=readme-ov-file#smart-proxy-plugin-test has an example

[ekohl]

We are in the process of dropping Ruby 2.7. If we introduce a container I'd prefer it to use Ruby 3