Implement database connection pooling for Cardano transaction store

[jpraynaud]

Content

This PR includes the implementation of a database connection pooling for the store of the Cardano transaction repository.

Benchmarks

Total Requests	Concurrency	Transactions/Request	MKMap Pool (x50): Request/s	MKMap Pool (x50) + Database connection pool (x10): Request/s
1000	100	1	1385.94	8021.69
1000	100	2	478.92	4465.24
1000	100	3	297.35	2820.16
1000	100	4	257.99	2517.21
1000	100	5	165.21	1588.88
1000	100	6	141.69	1424.89
1000	100	7	115.37	1209.83
1000	100	8	108.2	1110.13
1000	100	9	87.5	937.6
1000	100	10	84.58	903.11
1000	100	20	38	427.45
1000	100	30	29.33	319.36
1000	100	40	23.75	257.53
1000	100	50	18.13	191.57
1000	100	60	15.39	161.08
1000	100	70	12.76	138.76
1000	100	80	11.15	119.57
1000	100	90	10.25	110.43
1000	100	100	9.15	98.07

Running on Linux / 8 cores / 64 GB RAM / 2 TB SSD

Pre-submit checklist

• Branch
  • [x] Tests are provided (if possible)
  • [x] Crates versions are updated (if relevant)
  • [x] CHANGELOG file is updated (if relevant)
  • [x] Commit sequence broadly makes sense
  • [x] Key commits have useful messages
• PR
  • [x] No clippy warnings in the CI
  • [x] Self-reviewed the diff
  • [x] Useful pull request description
  • [x] Reviewer requested
• Documentation
  • [x] Update documentation website (if relevant)

Issue(s)

Closes #1760

[github-actions[bot]]

Test Results

    4 files  ±0     51 suites  ±0   8m 39s :stopwatch: ±0s 1 079 tests +1  1 079 :white_check_mark: +1  0 :zzz: ±0  0 :x: ±0  1 227 runs  +1  1 227 :white_check_mark: +1  0 :zzz: ±0  0 :x: ±0 

Results for commit c153037c. ± Comparison against base commit 727e7cde.

:recycle: This comment has been updated with latest results.