perf: use orjson in metrics

[anonrig]

We have enough confidence to say that orjson doesn't cause any errors/issues. We can now safely get rid of json and rapidjson in our repository.

Ref: https://github.com/getsentry/sentry/issues/68903

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.75000% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.97%. Comparing base (7572953) to head (e1f79d5). Report is 1001 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #70572      +/-   ##
==========================================
+ Coverage   79.96%   79.97%   +0.01%     
==========================================
  Files        6501     6505       +4     
  Lines      290476   290670     +194     
  Branches    50044    50102      +58     
==========================================
+ Hits       232278   232472     +194     
  Misses      57831    57831              
  Partials      367      367              

Files	Coverage Δ
src/sentry/sentry_metrics/client/kafka.py	97.67% <100.00%> (ø)
...ntry/sentry_metrics/consumers/last_seen_updater.py	100.00% <100.00%> (ø)
...etrics/querying/metadata/metrics_code_locations.py	100.00% <100.00%> (ø)
...ntry/sentry_metrics/visibility/metrics_blocking.py	93.84% <88.88%> (-0.56%)	:arrow_down:

... and 206 files with indirect coverage changes

[anonrig]

Changes on our code LGTM, thanks for doing this!

Does any of these paths generate a JSON object with integer as the key?

[getsantry[bot]]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

---

"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀