docs: updated documentation for MVC component.

[Teebarh]

This PR brings over the documentation for the MVC component, updates it to include new additions, and converts the format to reStructuredText (RST).

It addresses issue #99.

[RCheesley]

@Teebarh please take a look at the failing build job. It gives you some insights into why you cannot see the MVC item on the menu.

[Teebarh]

Okay, I'll give it a look.

[RCheesley]

Hi @Teebarh please review the feedback from @escopecz in the commit here: 5b0b900#r158199455

As I mentioned, this whole section needed to be reviewed and updated while reviewing the Mautic codebase, because we use Twig now instead of PHP views, and a whole lot of stuff has changed (e.g. using dependency injection).

So this PR needs to be updated to consider that, and provide the appropriate documentation accordingly.

[Teebarh]

I'll check it out and revert back accordingly. Thank you, Ruth!

[adiati98]

@escopecz @shinde-rahul, can anyone help me to review the content here whenever you have time? TIA! ✨

[adiati98]

@mautic/core-team @RCheesley some links here aren't the same links that are used in the legacy docs. So, I'd like to confirm.

Also, most of our dev docs aren't in the same structure as the legacy. Some pages are combined (maybe because the contents per page are short?) and I don't know if they're correct. I need more info on how we'd like to structure the dev docs.

TIA! ✨

[escopecz]

Thanks!