Simplify how git repositories are opened

[lunny]

Purpose

This is a refactor toward building an abstraction over managing git repositories.
Afterwards, it does not matter anymore if they are stored on the local disk or somewhere remote.

What this PR changes

We used git.OpenRepository everywhere previously.
Now, we should split them into two distinct functions:

Firstly, there are temporary repositories which do not change:

git.OpenRepository(ctx, diskPath)

Gitea managed repositories having a record in the database in the repository table are moved into the new package gitrepo:

gitrepo.OpenRepository(ctx, repo_model.Repo)

Why is repo_model.Repository the second parameter instead of file path?
Because then we can easily adapt our repository storage strategy.
The repositories can be stored locally, however, they could just as well be stored on a remote server.

Further changes in other PRs

• A Git Command wrapper on package gitrepo could be created. i.e. NewCommand(ctx, repo_model.Repository, commands...). git.RunOpts{Dir: repo.RepoPath()}, the directory should be empty before invoking this method and it can be filled in the function only. Move git command run on a special repository to standalone methods to hide the implemention detail #28940
• Remove the RepoPath()/WikiPath() functions to reduce the possibility of mistakes.

[wolfogre]

I think it's a good idea to do this; however, I'm afraid it's not enough.

The package git also exposes other functions that accept paths, like:

• GetBranchesByPath(ctx context.Context, path string, skip, limit int),
• GetBranchCommitID(ctx context.Context, path, branch string)
• RepositoryFromContextOrOpen(ctx context.Context, path string)

I believe all of them should be removed to prevent misuse and keep only git.OpenRepository(ctx, diskPath) for gitrepo.

[lunny]

I think it's a good idea to do this; however, I'm afraid it's not enough.

The package git also exposes other functions that accept paths, like:

* `GetBranchesByPath(ctx context.Context, path string, skip, limit int)`,

* `GetBranchCommitID(ctx context.Context, path, branch string)`

* `RepositoryFromContextOrOpen(ctx context.Context, path string)`

I believe all of them should be removed to prevent misuse and keep only git.OpenRepository(ctx, diskPath) for gitrepo.

Done.

[wxiaoguang]

I've no idea about whether the design is good enough, some points look really strange to me.

But at least, I do not think it is right to introduce a dependency between modules/gitrepo and models/repo. Isn't there already a guideline saying to avoid making modules calls models? To make the code maintainable, it could use some interfaces, eg: interface { GitRepoStoragePath() string }

[lunny]

@wxiaoguang @delvh Introduce an interface respository and removed the dependency on respotiroy package.

[lunny]

I've no idea about whether the design is good enough, some points look really strange to me.

But at least, I do not think it is right to introduce a dependency between modules/gitrepo and models/repo. Isn't there already a guideline saying to avoid making modules calls models? To make the code maintainable, it could use some interfaces, eg: interface { GitRepoStoragePath() string }

There is no design currently. It's just refactor to move all managed git repositories operations into the single package to make further implementation easier.