feat: Add bulk-upload util

[lcian]

This is a utility that mirrors the sentry-cli snapshots upload command for easy sandbox tests.
It can be used in sandbox with the preprod manifest committed here: https://github.com/getsentry/terraform-sandboxes.private/pull/513/changes.
Tune the parameters, then run kubectl apply -f tests/preprod/manifest.yaml.
The snapshots are already mounted at /data/preprod, so no need to do anything there. They've been generated with a distribution having p50 == 10 KiB, p99 == 215 KiB.

You likely want to tune the parameters limit (to not work on all the 40k files, just a subset), head_first, individual_concurrency, batch_concurrency (if you don't set the last 2, the defaults from objectstore_client will be used, which matches what Sentry CLI uses).

The prefix parameter can also be useful when performing multiple tests: the first run will populate the objects in Objectstore; if you don't set a prefix, you will (head and) override existing objects, which might result in a slightly different benchmark from fresh inserts.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 169 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.41%. Comparing base (65c8eaf) to head (80068ab).

Files with missing lines	Patch %	Lines
bulk-upload/src/main.rs	0.00%	169 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #561      +/-   ##
==========================================
- Coverage   87.40%   86.41%   -1.00%     
==========================================
  Files          93       94       +1     
  Lines       14787    14956     +169     
==========================================
- Hits        12925    12924       -1     
- Misses       1862     2032     +170     

Components	Coverage Δ
Rust Backend	92.22% <ø> (-0.01%)	⬇️
Rust Client	79.89% <ø> (ø)
Python Client	90.20% <ø> (ø)

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