Fix insert link in content editor

What does this MR do and why?

Standardize inserting links in content editor and also add a shortcut to insert links

Fixes issues:

• !116390 (comment 1339728603)
• When clicking on top bar dropdown with content ... (#406738 - closed)
• When switching between link and image in conten... (#406737 - closed)
• Clarify editing the title of a link in the Cont... (#366735 - closed)
• Create links in the Content Editor using a keyb... (#334189 - closed)

Screenshots or screen recordings

Before	After
Screen_Recording_2023-04-03_at_22.01.20	Screen_Recording_2023-04-12_at_16.31.35

How to set up and validate locally

1. Access content editor. Content editor (rich text editor) is available in wikis globally, and in issue/MR comments behind a feature flag :content_editor_on_issues. Click "Viewing markdown" at bottom right and select "Rich text" from the menu to switch to content editor.
2. Click the button in the toolbar to insert a link, or press Cmd+k to insert it

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.