Implement connection pooling

[DanPaseltiner]

PULL REQUEST

Summary

This PR introduces connection pooling in the MPI. This required making the following changes:

1. The DAL and MPI expose the pool_size and max_overflow sqlalchemy parameters
2. link_record_against_mpi expects the connection client to be passed in as a parameter allowing a single connection pool to be utilized for multiple linkage requests

Related Issue

Fixes #CDCgov/phdi-azure#326

Checklist

• If this code affects the other scrum team, have they been notified? (In Slack, as reviewers, etc.)

[m-goggins]

Looks good! I'm glad you found a way to make the testing easier

[codecov]

Codecov Report

Merging #908 (68b8b63) into main (ed4eeae) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #908      +/-   ##
==========================================
- Coverage   96.38%   96.38%   -0.01%     
==========================================
  Files          48       48              
  Lines        2821     2820       -1     
==========================================
- Hits         2719     2718       -1     
  Misses        102      102              

Flag	Coverage Δ
unit-tests	96.38% <100.00%> (-0.01%)	⬇️

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

Files	Coverage Δ
phdi/linkage/dal.py	97.08% <100.00%> (ø)
phdi/linkage/link.py	97.11% <100.00%> (ø)
phdi/linkage/mpi.py	96.11% <100.00%> (-0.03%)	⬇️