Nidx: Support for S3 endpoint TLS validation option

[zepellin]

This pull request introduces support for configuring SSL certificate verification for S3-compatible object storage backends in the nidx chart and backend. It updates Helm chart values and documentation to expose the verify_ssl option, modifies the Rust backend to pass this setting to the S3 client, and adds tests to ensure correct parsing and behavior.

Helm chart and configuration improvements:

• Updated charts/nidx/README.md and charts/nidx/values.yaml to document and expose the verify_ssl option for both indexer and storage S3 object store configurations, allowing users to enable or disable TLS certificate verification via environment variables. [1] [2]

Backend (Rust) enhancements:

• Added an optional verify_ssl field to the ObjectStoreKind::S3 variant in nidx/src/settings.rs, and updated the S3 client builder to respect this setting, disabling certificate verification when requested. [1] [2] [3]

Testing and reliability:

• Added unit tests to nidx/src/settings.rs to verify correct parsing of the verify_ssl setting from both JSON and environment variables, and to ensure the default behavior is to enable certificate verification. [1] [2]### Description
  Describe the proposed changes made in this PR.

How was this PR tested?

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[codecov]

Codecov Report

❌ Patch coverage is 63.88889% with 13 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.22%. Comparing base (01e1074) to head (63f6b63).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
nidx/src/settings.rs	63.88%	12 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3644      +/-   ##
==========================================
- Coverage   85.23%   85.22%   -0.01%     
==========================================
  Files         564      564              
  Lines       48508    48542      +34     
  Branches    14221    14255      +34     
==========================================
+ Hits        41346    41371      +25     
- Misses       6547     6555       +8     
- Partials      615      616       +1     

Flag	Coverage Δ
nidx	80.00% <63.88%> (-0.03%)	⬇️
nucliadb	73.48% <ø> (+<0.01%)	⬆️
nucliadb-ingest	43.60% <ø> (-0.02%)	⬇️
nucliadb-reader	43.62% <ø> (-0.02%)	⬇️
nucliadb-search	54.05% <ø> (ø)
nucliadb-standalone	46.00% <ø> (ø)
nucliadb-train	44.68% <ø> (ø)
nucliadb-writer	46.93% <ø> (-0.02%)	⬇️
nucliadb_dataset	73.65% <ø> (ø)
nucliadb_models	71.55% <ø> (ø)
nucliadb_sdk	83.08% <ø> (ø)
nucliadb_telemetry	72.33% <ø> (ø)
nucliadb_utils	80.94% <ø> (ø)

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