feat(clipboard): allow overriding clipboard and document OSC52 example

[kraftnix]

Unlike the original parent of this fork, it is not currently possible to use a different copy/clipboard command (which used to be implemented via action_callback).

This PR adds a way to override the default copy command, which can be used to add OSC52 support (or use a specific clipboard program like wl-copy).

Test Platforms

• windows
• macOS
• linux

Test Hosts

• Test on github.com.
• Test on gitlab.com.
• Test on bitbucket.org.
• Test on codeberg.org.
• Test on git.samba.org.

Test Functions

• Use GitLink(!) to copy git link (or open in browser).
• Use GitLink(!) blame to copy the /blame link (or open in browser).
• Use GitLink(!) default_branch to open the /main//master link in browser (or open in browser).
• Use GitLink(!) current_branch to open the current branch link in browser (or open in browser).
• Copy git link in a symlink directory of git repo.
• Copy git link in an un-pushed git branch, and receive an expected error.
• Copy git link in a pushed git branch but edited file, and receive a warning says the git link could be wrong.
• Copy git link with 'file' and 'rev' parameters.

[linrongbin16]

This feature looks great, thank you, will take a look later

[linrongbin16]

I will fix the lint issue in ci.

---

Done in e4cdebb

[linrongbin16]

hi @kraftnix ,

This part is like a cycle-dependency between "gitlinker.actions" and "gitlinker.configs".

I moved this part to "setup" here: https://github.com/linrongbin16/gitlinker.nvim/pull/280/files#diff-e85b0a73f385d3b9be62752dbc0afd2ca8eba8b75c12d7667a5514b8b35755ee

[kraftnix]

Looks good! I wasn't quite sure where to put the override when testing before.