(mysql) use async/await instead promises on connection

[chrisllontop]

Please check if the PR fulfills these requirements

• Followed the Contributing guidelines.
• Tests for the changes have been added (for bug fixes/features) with 100% code coverage.
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (deb58a2) 100.00% compared to head (e44d63e) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #840   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         2519      2541   +22     
  Branches       303       328   +25     
=========================================
+ Hits          2519      2541   +22     

Impacted Files	Coverage Δ
packages/mysql/src/index.ts	100.00% <100.00%> (ø)

... and 4 files with indirect coverage changes

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