[IMPROVE] Support Markdown on Livechat Custom Message Setting

[murtaza98]

Proposed changes (including videos or screenshots)

Since we're now adding support for markdown text on Livechat offline Instructions message, we're adding this PR to provide a markdown editor in place of the generic text setting for the corresponding livechat setting

Issue(s)

Steps to test or reproduce

Further comments

Note: I've moved the Markdown components I needed for this PR out of the EE folder and into our general community folder since this setting is also present on community version

[github-actions]

You have added 1 .js files, please convert to ts(x).
client/views/admin/settings/inputs/MarkdownSettingInput.stories.js

js files removed

[KevLehman]

It works 🤔 but I feel the interaction a bit buggy

• Cut (ctrl-x) sometimes work, sometimes doesn't
• Link button doesn't work
• Sometimes, when deleting a long text, you're left with just one character that you cannot remove

[CLAassistant]

All committers have signed the CLA.