Add the MINLP solver MAiNGO to the documentation

[MAiNGO-github]

We have recently built a wrapper around our open-source global MINLP solver MAiNGO, which is is written in C++.
The wrapper initially took a lot of inspiration from the Baron.jl repository.

Looking at the checklist, the conditions for including the solver in the documentation should be fulfilled.

We would be very excited to be included in the list of compatible solvers.

https://github.com/MAiNGO-github/MAiNGO.jl

Basic

• Check that the solver is a registered Julia package
• Check that the solver supports the long-term support release of Julia
• Check that the solver has a MathOptInterface wrapper
• Check that the tests call MOI.Test.runtests. Some test excludes are
  permissible, but the reason for skipping a particular test should be
  documented.
• Check that the README and/or documentation provides an example of how to
  use the solver with JuMP

Documentation

• Add a new row to the table in docs/src/installation.md

Optional

• Add package metadata to docs/packages.toml

[odow]

Nice! Let me take a look

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.35%. Comparing base (a9b5ff9) to head (096097d).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3696      +/-   ##
==========================================
- Coverage   98.36%   98.35%   -0.02%     
==========================================
  Files          43       43              
  Lines        5699     5707       +8     
==========================================
+ Hits         5606     5613       +7     
- Misses         93       94       +1     

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[odow]

I'm going to mark this as blocked by MAiNGO-github/MAiNGO.jl#2, but it looks nice!

Pleased you figured out the Yggdrasil stuff 😄

[MAiNGO-github]

@odow
I added the Github actions.
I also incorporated a recent improvement from Baron.jl

There also were spellchecking warnings. I fixed those that were correct. Some are caused by how our README is set up.
In case this is blocking or annoying, I would suggest not adding to docs/packages.toml, but only to the overview table.