docs: move benchmark tool docs

[fuyufjh]

What's changed and what's your intention?

Move docs/developer/benchmark_tool/state_store.md to rust/bench/ss_bench/README.md.

Checklist

N/A

Refer to a related PR or issue link (optional)

None

[Sunt-ing]

Please change the link mentioned in rust/bench/ss_bench/main.rs

[codecov]

Codecov Report

Merging #1513 (b98b4bc) into main (b00df18) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##               main    #1513      +/-   ##
============================================
+ Coverage     70.44%   70.45%   +0.01%     
  Complexity     2766     2766              
============================================
  Files          1031     1031              
  Lines         90471    90493      +22     
  Branches       1790     1790              
============================================
+ Hits          63735    63761      +26     
+ Misses        25845    25841       -4     
  Partials        891      891              

Flag	Coverage Δ
java	61.01% <ø> (ø)
rust	72.46% <ø> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
rust/bench/ss_bench/main.rs	0.98% <ø> (ø)
rust/frontend/src/expr/subquery.rs	48.27% <0.00%> (-3.58%)	⬇️
rust/sqlparser/src/parser.rs	92.63% <0.00%> (+0.04%)	⬆️
...rontend/src/optimizer/plan_node/logical_project.rs	97.24% <0.00%> (+0.04%)	⬆️
rust/sqlparser/src/tokenizer.rs	93.61% <0.00%> (+0.11%)	⬆️
...st/frontend/src/optimizer/plan_node/logical_agg.rs	97.63% <0.00%> (+0.20%)	⬆️
.../src/executor/managed_state/aggregation/extreme.rs	90.40% <0.00%> (+0.27%)	⬆️
rust/frontend/src/binder/expr/binary_op.rs	93.93% <0.00%> (+3.03%)	⬆️

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[skyzh]

We can also have ToCs for READMEs of independent tools in CONTRIBUTING.md. IIRC, we have ss_bench, risedev, and planner-test

[TennyZhuang]

LGTM