Document ObjectStoreProvider

[tustvold]

Which issue does this PR close?

Closes #.

Rationale for this change

Adds some documentation, r.e. #3595

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #3619 (39584b5) into master (ebb28f5) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3619      +/-   ##
==========================================
- Coverage   86.07%   86.07%   -0.01%     
==========================================
  Files         300      300              
  Lines       56314    56337      +23     
==========================================
+ Hits        48473    48492      +19     
- Misses       7841     7845       +4     

Impacted Files	Coverage Δ
datafusion/core/src/datasource/object_store.rs	85.05% <ø> (ø)
datafusion/expr/src/window_frame.rs	92.43% <0.00%> (-0.85%)	⬇️
datafusion/optimizer/src/simplify_expressions.rs	82.67% <0.00%> (-0.01%)	⬇️
datafusion/expr/src/logical_plan/plan.rs	77.26% <0.00%> (+0.16%)	⬆️

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[yahoNanJing]

LGTM

[ursabot]

Benchmark runs are scheduled for baseline = 7325b83 and contender = ea3dbb6. ea3dbb6 is a master commit associated with this PR. Results will be available as each benchmark for each run completes.
Conbench compare runs links:
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ec2-t3-xlarge-us-east-2] ec2-t3-xlarge-us-east-2
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on test-mac-arm] test-mac-arm
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-i9-9960x] ursa-i9-9960x
[Skipped ⚠️ Benchmarking of arrow-datafusion-commits is not supported on ursa-thinkcentre-m75q] ursa-thinkcentre-m75q
Buildkite builds:
Supported benchmarks:
ec2-t3-xlarge-us-east-2: Supported benchmark langs: Python, R. Runs only benchmarks with cloud = True
test-mac-arm: Supported benchmark langs: C++, Python, R
ursa-i9-9960x: Supported benchmark langs: Python, R, JavaScript
ursa-thinkcentre-m75q: Supported benchmark langs: C++, Java