[tiptap] Insert and edit Links

[kulmann]

User story

• As a user I want to be able to insert and edit links in the text editor, so that I can link to external websites.

User value

Text editing feature completeness.

Acceptance criteria

• Inserting a link is possible for markdown, html and tiptap-json content strategies
• Pasting a link into the text editor automatically makes it a link
• Clicking the link opens an inline link panel (see below)
• Clicking the link does NOT follow the link
• The toolbar has a link icon, which opens an inline link panel (see below)
• The slash command menu has a link entry, which opens an inline link panel (see below)
• The inline link panel has two text fields: url and text, a button for following the link and a button for unlinking the text (similar to how platejs is doing it)