[docs] Add SDPLR to list of solvers

[blegat]

I'm already opening this PR even if it's not released to see if the README passes the tests

Basic

• [x] Check that the solver is a registered Julia package, needs https://github.com/blegat/SDPLR.jl/pull/19
• [x] Check that the solver supports the long-term support release of Julia
• [x] Check that the solver has a MathOptInterface wrapper
• [x] Check that the tests call MOI.Test.runtests. Some test excludes are permissible, but the reason for skipping a particular test should be documented.
• [x] Check that the README and/or documentation provides an example of how to use the solver with JuMP

Documentation

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

Optional

• [x] Add package metadata to docs/packages.toml

cc @sburer

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (232a95d) 98.28% compared to head (90394bc) 98.28%. Report is 4 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #3644 +/- ## ======================================= Coverage 98.28% 98.28% ======================================= Files 43 43 Lines 5640 5640 ======================================= Hits 5543 5543 Misses 97 97 ```

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[odow]

I wonder if we should move it to jump-dev before tagging.