Remove the need to pass an account to getFallbackUrlForProxyResolve

[niik]

xref #18586

Description

This is almost exclusively a refactor PR (notable exception is deleteRemoteBranch). We're trying to remove account from withAuthenticatingUser such that can freely modify (or remove) the getGenericHostname in order to be able to store more than one credential per host.

Prior to this PR getFallbackUrlForProxyResolve required an IGitAccount to resolve the url to use for resolving a proxy. That IGitAccount came all the way from withAuthenticatingUser and was resolved either by looking up the GitHubRepository associated with a Repository and using its endpoint to resolve an Account (which would then have the same endpoint) or by using the currentRemote of the repository to look up a generic account. We've tried to replicate this in getFallbackUrlForProxyResolve while removing the need for an account.

The deleteRemoteBranch method exception is that it would previously always make a call out to git remote in order to look up the current remote. With this refactor we're using the already loaded remotes from the GitStore to avoid that invocation (though we fall back to invoking if the gitStore doesn't have the remote we need).

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Release notes

Notes: