kakoune: use str for hooks and check configuration

[lobre]

Description

This is a follow-up on #3418.

The aim is to turn kakoune hooks into a string instead of an enum to avoid having to update them when they change in kakoune.

And to validate that the string value is correct, the idea was to add a configuration checker in the checkPhase.

However, I struggled to correctly implement the checker as kakoune does not have a simple way to validate the configuration.

See my comment for more details: #3418 (comment)

As I am not using kakoune anymore, I am simply creating this PR to reference the WIP that has been done, in case someone wants to continue working on this.

I will be directly closing the PR, but feel free to comment if you are interested.

[lobre]

As said above, closing. Feel free to comment if you want to pick it up.