Spanner bulk data migration: Support Bool as a primary key by mapping it to IndexType.Numeric

[nmemond]

This is a copy of #3045 but up-to-date with main, because that developer is out of office for the rest of the year and I don't have permissions to push to their fork.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.83%. Comparing base (fa4c196) to head (495fb56).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3112      +/-   ##
============================================
+ Coverage     50.48%   55.83%   +5.35%     
+ Complexity     5040     1634    -3406     
============================================
  Files           973      471     -502     
  Lines         59721    26474   -33247     
  Branches       6511     2775    -3736     
============================================
- Hits          30149    14783   -15366     
+ Misses        27443    10794   -16649     
+ Partials       2129      897    -1232     

Components	Coverage Δ
spanner-templates	71.83% <100.00%> (+1.09%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	80.06% <ø> (-0.04%)	⬇️
spanner-live-reverse-replication	77.79% <ø> (-0.04%)	⬇️
spanner-bulk-migration	88.21% <100.00%> (-0.03%)	⬇️

Files with missing lines	Coverage Δ
...jdbc/dialectadapter/mysql/MysqlDialectAdapter.java	99.62% <100.00%> (+<0.01%)	⬆️

... and 521 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.