Not adding to Allowed HTML Tags

Problem/Motivation

The HTML tags and attributes in templates are not added to the Allowed HTML Tags and thus do not work, unless the Source plugin is added with its Manually Editable HTML Tags.

Steps to reproduce

Add CKEditor5 Template to a text format. Do not add the Source button to the same text format.
Create a template with HTML or attributes that are not in the text format's allowed HTML Tags
Add the template to a text field on a page with that text format
The tags or attributes not in the allowed HTML tags are stripped.

Proposed resolution

Three possible solutions:

1. Add a field similar to Manually Editable Tags to add them manually. Use this to add to allowed HTML tags.
2. Add a section to the json file that defines tags and attributes used by the templates. Use to add to allowed HTML tags
3. Scan the templates to look for tags and attributes to be added to allowed HTML tags

Remaining tasks

Decide and implement.

User interface changes

Ideally none (the last option)

API changes

None

Data model changes

Ideally none (the last option)