refactor(instr-mysql2): use exported strings for attributes

[david-luna]

Which problem is this PR solving?

• Updates Update usage of semantic conventions to new exported strings #2025

Short description of the changes

• Update @opentelemetry/semantic-conventions to ^1.22
• Replace SemanticAttributes.* with exported strings SEMATTRS_*
• Update README with new semantic convention package version and key

[codecov]

Codecov Report

Merging #2115 (7d4aa8b) into main (dfb2dff) will decrease coverage by 0.32%.
Report is 59 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2115      +/-   ##
==========================================
- Coverage   90.97%   90.66%   -0.32%     
==========================================
  Files         146      147       +1     
  Lines        7492     7584      +92     
  Branches     1502     1517      +15     
==========================================
+ Hits         6816     6876      +60     
- Misses        676      708      +32     

Files	Coverage Δ
...etry-instrumentation-mysql2/src/instrumentation.ts	94.73% <ø> (ø)
.../opentelemetry-instrumentation-mysql2/src/utils.ts	96.96% <100.00%> (ø)

... and 9 files with indirect coverage changes