Add explict setting for APP vs PAT auth

[danfoster]

Description

I don't want the helm chart to manage the secret with PAT/APP details, because I manage secrets via sealedSecrets.
In theory this is fine, as I can just leave githubPat and githubApp* values blanks and the chart won't create the secret and I can just refer to an existing secret.

But the condition if to include the GITHUB_APP* or GITHUB_PAT env vars in the Deployment is conditional on one of these being set. So this makes it impossible to include the env vars without it also managing the secret.

The approach I've taken here is to create a new value: authType, which is either app or pat. This is used to decide which env vars to expose. This allows us to expose an externally managed secret for either.

But this will be a breaking change, as every user will need to set this value. Not sure if there's a better way to manage this?

Related Issue(s)

Checklist

• This PR includes a documentation change
• This PR does not need a documentation change

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• This PR includes test changes
• This PR's changes are already tested

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• This change is not user-facing
• This change is a patch change
• This change is a minor change
• This change is a major (breaking) change

Changes made