[FEATURE] Adding custom GrapeJS plugins to customize the editor

[irfanhanfi]

Q	A
Bug fix? (use the a.b branch)	[ ]
New feature/enhancement? (use the a.x branch)	[ ]
Deprecations?	[ ]
BC breaks? (use the c.x branch)	[ ]
Automated tests included?	[ ]
Related user documentation PR URL	mautic/mautic-documentation#...
Related developer documentation PR URL	mautic/developer-documentation#...
Issue(s) addressed	Fixes #...

Description:

Creating a clone PR of #12429 for Mautic 4.4

[escopecz]

I don't think this will be merged to Mautic 4. It's a feature and only bug and security fixes will be accepted for future Mautic 4 releases.

cc @mollux @RCheesley

[ekkeguembel]

That's ok, we can even close it. We decided to do the PR anyway, so people who are on m4 can take advantage of it by applying it as a patch.
And at the same time, some experience will be collected, including foundation for any discussion about having this feature in m5.
cc @mollux @RCheesley

[RCheesley]

Thanks for making the PR for Mautic 4 - let's close the PR as we won't be able to merge it, but it will be there as a reference point if people want this feature backported for their own instances.