Add ckeditor5-html-embed plugin

[ChristophWurst]

Rebased version of #7298.

[ChristophWurst]

How it looks

[AlexanderZuehr]

@ChristophWurst
I dont know why it is so small in the beginning. It was the same for me.
I fixed it temporarily by using the Nextcloud CSS APP with

#select, button:not(.button-vue), input, textarea, div[contenteditable="true"], div[contenteditable="false"]{ width: unset; }

not it looks like this for me.

I am not skilled enough to fix the standard behavior.

[ChristophWurst]

I will have to discuss this with our designers then. I was under the impression that the HTML plugin would allow the users to edit the sources of the full message. Instead, it allows users to insert a block of HTML.

[ChristophWurst]

@nimishavijay @jancborchardt what do you think about this change? The feature was briefly discussed in #7282.

[AlexanderZuehr]

Yes it inserts a block. For my company that is exactly the feature we need and it is working quite good.
For Example:

Creating a signature.

Writing an email, signature is added and shown perfectly.

Also other users see the signature as intended.

I know that html signatures are not not very popular, but our company relies on it.

[AlexanderZuehr]

@ChristophWurst Hey, is there any chance my Pull request will be or maybe is accepted?

[technikfrek]

Is there any progress?
Me and my company are also interested in this feature.

Thanks in advance!

[ChristophWurst]

Closing for now. I need designers to sign off this change. It still doesn't look like the right way to do this, sorry.

Ref #7427 (comment)