[FEAT] Add Recursive Bulk Initialize and Update for Submodules

[cesarandr]

• PR Description
  This PR adds a new bulk action for submodules.
  As I often work with a lot of submodules that are hierarchically structured, the flag "--recursive" saves a lot of work.

• Please check if the PR fulfills these requirements

• Cheatsheets are up-to-date (run go generate ./...)
• Code has been formatted (see here)
• Tests have been added/updated (see here for the integration test guide)
• Text is internationalised (see here)
• If a new UserConfig entry was added, make sure it can be hot-reloaded (see here)
• Docs have been updated if necessary
• You've read through your own file changes for silly mistakes etc

[stefanhaller]

Looks mostly good, except that the third commit needs to be squashed into the second, because otherwise the second commit doesn't compile. (Actually I think you might as well squash all three commits, but I'll leave that to you to decide.)

As for the feature itself: while it makes sense to have it in that menu for completeness, I don't think it is convenient enough for daily use. I need to update submodules recursively all the time at work, and I'm not going to switch to the submodules tab, open a menu and then invoke a command from there; that's way too many keystrokes for something that I need to do really often. Also, I'm usually in the Files panel when I see that the submodules are out of date, so I want to fix that right there, and stay there. I have a custom command for this that I can invoke from everywhere:

customCommands:
- key: "U"
  command: "git submodule update --init --recursive"
  context: "global"
  description: "Update submodules"
  loadingText: "Updating Submodules..."
  stream: true

[cesarandr]

So I can also use this custom action as well!
In case the use for this rises and other users want a feature like that we can leave the PR open.
If this is not wanted, we can also close this PR.

[stefanhaller]

Looks good, thanks. As I said, I'm not opposed to adding this command, it does make sense to have it for completeness. Merging.

For future contributions: please don't merge master into your branch; rebase onto master instead, this results in a cleaner commit history. (I did it for this branch now).

[cesarandr]

Thanks for merging, next time I will keep this in mind. Thanks a lot for your help!