Add dialog to install EFI bootloader to removable location

[mintsuki]

This is just for GRUB and Limine for now.

[svartkanin]

i think this should go under a new Bootloader sub-menu instead of a global namespace setting.
The current bootloader selection should go in there together with this setting

[mintsuki]

The PR should be ready for review now.

Please, beware that I have used LLMs for most of these changes due to my unfamiliarity with the codebase, and while I have reviewed and tested the code, I would strongly recommend someone familiar with the codebase to thoroughly review the changes.

[mintsuki]

@svartkanin alright, sorry, I added a bunch more commits, but I should be done now, at least for what this PR is concerned.

[mintsuki]

Anything else I should change before approval?

[svartkanin]

Sorry I was too busy, I tested the code and it seems to work, great job in making the config backwards compatible.
I left some small comments if you can address those then we can merge the PR