RTE classes for Buttons not valid in Link Browser

# Bug Report

## Prerequisites

* [ ] Can you reproduce the problem on TYPO3 v11.5 LTS
* [x] Can you reproduce the problem on TYPO3 v12.4 LTS
* [x] Did you [perform a cursory search](https://github.com/issues?q=is%3Aissue+user%3Abenjaminkott+repo%3Abenjaminkott%2Fbootstrap_package)
to see if your bug or enhancement is already reported?

## Description

Noticed while I searched for the Bootstrap Buttons

## Steps to Reproduce

1. Create Link in RTE
2. Mark it as Block Type "Button" (no matter which)
3. click the link and open the Link Browser
4. Drop Down for CSS class shows that current value is not allowed

### Expected behavior

All CSS classes that can be applied to links via RTE should be valid in Link browser

### Actual behavior

### Screenshots


## Versions
bootstrap_package: [14.0.7]

Reproduce the issue in TYPO3 v12.4 with bootstrap_package 14.0.7 by creating an RTE link, selecting a Button block type, and opening the Link Browser. Trace the RTE and Link Browser CSS-class configuration; done means every CSS class available to links in the RTE is accepted by the Link Browser dropdown.

Written by the indexing model from the issue text.