ratelimit: impl BBR-like algorithm

[CabinfeverB]

What problem does this PR solve?

Issue Number: ref #7167
should be merged after #7239

What is changed and how does it work?

We implmented a BBR like algorithm.

1. Divide the time window into multiple time buckets of equal duration. Initialize a counter for each time bucket to keep track of the concurrency change.

2. Monitor the concurrency of requests. When request comes, increment the counter of arrival time bucket. When processed request, decrease the counter of pass time bucket.

3. Monitor the amount of pass requests. When processed request, increment the counter.

4. Record the processing duration.

5. Periodically, check the counters in each time bucket to analyze the concurrency change. If the value of any counter increases continuously over a certain threshold for a consecutive number of time buckets, it indicates the API is reaching its maximum concurrency:

   • We divided the time window into multiple time buckets and counted the change of concurrency in each time bucket.

$$ \sum_{i=1}^{bucket_{size}} b_i \geq 1 $$

$$ p_i = \begin{cases} 1 &\text{if } b_i > 0\\ 0 &\text{if } b_i \leq 0\ \end{cases} $$

$$ n_i = \begin{cases} 1 &\text{if } b_i < 0\\ 0 &\text{if } b_i \geq 0\ \end{cases} $$

    For every 

$$ \forall i,  \sum_{j=1}^{i} p_i \geq \sum_{j=1}^{i} n_i $$

    And 

$$ \sum_{i=1}^{bucket_ size/2} b_i \geq 1 $$

6. According the maxinum pass request and minimum duration, calculate RDP and use it as conccurency limit.

Check List

Tests

• Unit test

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

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[codecov]

Codecov Report

Merging #7246 (b13305c) into master (37be34e) will increase coverage by 0.01%.
Report is 97 commits behind head on master.
The diff coverage is 94.81%.

❗ Current head b13305c differs from pull request most recent head 348076e. Consider uploading reports for the commit 348076e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7246      +/-   ##
==========================================
+ Coverage   73.47%   73.48%   +0.01%     
==========================================
  Files         432      433       +1     
  Lines       47842    48014     +172     
==========================================
+ Hits        35151    35285     +134     
- Misses       9648     9672      +24     
- Partials     3043     3057      +14     

Flag	Coverage Δ
unittests	73.48% <94.81%> (+0.01%)	⬆️

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PR needs rebase.

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