Document MySQL DSN password URL-encoding requirement

[josecelano]

Summary

Document that MySQL DSN passwords must be percent-encoded when they contain reserved URL characters.

Changes

• Add URL-encoding guidance to container deployment docs.
• Add URL-encoding note to the default MySQL tracker config example.
• Clarify MySQL DSN format in configuration docs and add encoding requirement for reserved characters.

Why

Deployments commonly build DSNs from environment variables. Generated secrets can include characters like + and /, which break DSN parsing unless encoded.

Fixes #1606

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.51%. Comparing base (d178b2b) to head (bcbef65).
⚠️ Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1692   +/-   ##
========================================
  Coverage    86.50%   86.51%           
========================================
  Files          288      288           
  Lines        22672    22672           
  Branches     22672    22672           
========================================
+ Hits         19613    19614    +1     
  Misses        2833     2833           
+ Partials       226      225    -1     

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[josecelano]

ACK bcbef65