git: add PushConfig to specify push config and add support for refspecs

[aryan9600]

Add PushConfig for configuring a push operation. Users can use PushConfig.Refspecs to specify the refspecs when using Push().

Furthermore, fix a bug related to Push() where all refs were pushed to origin, since we did not specify a refspec and the default refspec used by gogit is refs/heads/*:/refs/heads/*.

Add PushConfig.Force for force pushing and remove gogit.Client.forcePush in favor of the former.

Remove some stale test cases from TestSwitchBranch related to force push since we don't check if force pushing is enabled while switching branches anymore. Ref: #433

Part of: fluxcd/image-automation-controller#509

[hiddeco]

Think this approach will become difficult when we add support for push options, as there are now multiple methods which would require the additional option as an argument.

[aryan9600]

Main reason why I added a new function is that I didn't want to break the API. But your point regarding push options is certainly valid. How about we add a new type PushConfig which would store refspecs, options (in the future), etc. and change Push(ctx) error to Push(ctx, pushConfig) error?

[hiddeco]

The second option would be to introduce an option pattern, which wouldn't break the existing API from a consumer perspective except for breaking the interface.

[stefanprodan]

The git package is not v1 so I would not worry about breaking changes, let's chose the best UX even if it means changing the functions args.

[aryan9600]

If we don't have any problems breaking API, I don't see the harm in just passing the config object directly as an argument. It also follows the pattern for Clone() where we pass a CloneOptions object directly. One thing to note is that I suggested PushConfig on purpose as calling it PushOptions could (and probably would) lead to confusion given the existence of Git push options.

[hiddeco]

If we go that route, I would maybe even go as far as renaming CloneOptions to CloneConfig to be annoying once instead of annoying forever in terms of naming differences. But otherwise, this sounds good to me.

[aryan9600]

cool sounds good to me as well

[hiddeco]

LGTM, thank you @aryan9600 🙇

[aryan9600]

talked to @pjbgf offline and he's okay with the removal of the obsolete tests