feat: add uppercase transformation

[blotus]

The documentation mentions an uppercase transformation (https://coraza.io/docs/seclang/transformations/#uppercase), but it's not actually implemented in coraza.

This PR adds it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (93593ff) 82.58% compared to head (2ae6918) 82.59%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #935      +/-   ##
==========================================
+ Coverage   82.58%   82.59%   +0.01%     
==========================================
  Files         160      161       +1     
  Lines        8991     8997       +6     
==========================================
+ Hits         7425     7431       +6     
  Misses       1317     1317              
  Partials      249      249              

Flag	Coverage Δ
default	77.68% <100.00%> (+0.01%)	⬆️
examples	26.59% <16.66%> (-0.01%)	⬇️
ftw	47.01% <16.66%> (-0.03%)	⬇️
ftw-multiphase	49.21% <16.66%> (-0.03%)	⬇️
tinygo	75.21% <100.00%> (+0.01%)	⬆️

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[fzipi]

Thanks for your contribution!

LGTM. Unless @anuraaga has other opinions, it's good to merge.

[jptosso]

LGTM, but to keep testing consistency, can you also add the tests to internal/transformations/testadata?

https://github.com/corazawaf/coraza/blob/main/internal/transformations/testdata/lowercase.json

Thank you very much for your contribution.

[fzipi]

Thanks, merging now!