Make title appendix optional and changeable

I've added the option to leave the title attribute alone, but changing the string used requires an important cleanup of the module and the unit tests and should be dealt in a separate issue.

This will need an update hook

I have added the update hook into the install file. Thanks for the review!

This patch doesn't currently apply to the 2.0.2 release:
https://git.drupalcode.org/project/extlink/-/merge_requests/48.diff

Needed a slight rebase but works as expected

Automatically closed - issue fixed for 2 weeks with no activity.