Add a way to add spacing between sections

[codecat]

Is your feature request related to a problem? Please describe.
Something similar was requested in #876, which amounts to trying to add an mj-spacer in between 2 mj-section elements.

This is not guaranteed to work (even if it appears to work in my VSCode preview), but I don't think there's currently a good way to add spacing in between sections otherwise.

Describe the solution you'd like
I'd like to be able to (somehow) add spacing between sections. Perhaps even something like this (not exactly this terminology) could work:

<mj-list spacing="10">
  <mj-section />
  <mj-section />
</mj-list>

Describe alternatives you've considered
It's possible to add a border-bottom="10px solid #fff" to the bottom of the section, but that's not a great solution either.

Additional context

[iRyusa]

Hi ! I think the best "bulletproof" solution is to add an empty section with a padding. I'm not sure about how outlook will behave...

It's not pretty but this is what i'm using :

<mj-section padding-bottom="40px"><mj-column><mj-text>&nbsp;</mj-text></mj-column></mj-section>

Maybe we could add an attribute to mj-wrapper to add a flex-like "gap" between section that would do that 🤔

<mj-wrapper gap="20px"> 
  <mj-section />
  <mj-section />
</mj-wrapper>

[codecat]

I looked at mj-wrapper to see if it could do that exact thing, actually! So that sounds like the perfect place for it.