Enable RTE button "strike"

## Prerequisites

* [x] Can you reproduce the problem on TYPO3 v11.5 LTS
* [ ] Can you reproduce the problem on TYPO3 v12.4 LTS
* [x] Did you [perform a cursory search to see if your bug or enhancement is already reported?

## Description

I'd like to enable the "strike through" option in RTE, but this button is disabled in https://github.com/benjaminkott/bootstrap_package/blob/master/Configuration/RTE/Default.yaml#L128

I have my own YAML config for the RTE, which enhances the Default.yaml...

```
imports:
- { resource: "EXT:bootstrap_package/Configuration/RTE/Default.yaml" }
```

...but once a button is removed, it seems you can't enable it again.

### Expected behavior

I can use the useful and extensive configuration provided by EXT:bootstrap_package for RTE, but still I can overwrite this config.

### Actual behavior

I can't enable RTE buttons Strike, Anchor and Underline.

### Suggestion

Don't remove these three buttons.

Start with Configuration/RTE/Default.yaml at the referenced setting and review how the imported YAML is expected to be overridden by a project configuration. Confirm the behavior for Strike, Anchor, and Underline; done means those buttons are no longer removed and can be enabled by the importing configuration.

Written by the indexing model from the issue text.