fix(notification): Add application to githubStatus notification context

[dbrougham]

Add the application to the github status notification. This helps ensure checks are unique per service when working in a monorepo.

This functionality is behind the feature flag hasApplicationNameInContext to ensure backwards compatibility.

Issue: spinnaker/spinnaker#6442

[gregjones]

I think this will be quite disruptive for existing users of the feature - if the existing context has been set to required in the github branch-protection settings, then this will leave github waiting for statuses that never match the required value. I think that if the change is made at the end instead, then github will still match it, as a prefix. i.e. change it to pipeline/$pipeline/$application

[dbrougham]

Thanks for the feedback!

Yeah I did think that any repositories using this feature may be required to update their GitHub checks if they are set to required.

I couldn't seem to find anything online in the GitHub docs that mention a partial match working for the GitHub status. Will do some testing on this today.

Alternatively we could have a user specified context that is sent although this will require more code changes to implement, but would be backwards compatible, or we could look to use a feature flag to specify the full path for GitHub notification context

[dbrougham]

After some testing it doesn't look like the GitHub status will behave that way
https://docs.github.com/en/rest/reference/repos#statuses

We could add this to the release notes as a potential breaking change to be aware of?

Two alternate ways forward:

1. Put this functionality behind some kind of feature flag for echo detailedGitHubStatusNotification
2. Allow users to specify a custom context in the notification pipeline config/deck UI