Change admin notes from plain text to formatted text

Proposal

From !47825 (comment 524466470)

@dmoraBerlin said:

@harishsr is there a limitation of the text container/object; in that it needs to be plain text? Would it make sense to use a comment text box like in thread replies/comments to offer flexibility and unlimited characters?

Propose changing the admin notes to:

• use something that potentially allows unlimited characters
• provide basic formatting (such as line breaks)