Yaml: Add yaml syntax UT

[derrickaw]

1. Adding yaml syntax UT to verify that the yaml blueprints placed in the yaml folder are syntactically correct, since there will be occasions where we do not have 1:1 mappings with yaml templates.
2. mvn clean test -pl yaml -am

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.04%. Comparing base (6381f56) to head (ed510be).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2872      +/-   ##
============================================
- Coverage     50.06%   50.04%   -0.02%     
- Complexity     4972     5348     +376     
============================================
  Files           967      967              
  Lines         59329    59329              
  Branches       6448     6448              
============================================
- Hits          29702    29691      -11     
- Misses        27522    27533      +11     
  Partials       2105     2105              

Components	Coverage Δ
spanner-templates	70.44% <ø> (-0.05%)	⬇️
spanner-import-export	68.94% <ø> (-0.13%)	⬇️
spanner-live-forward-migration	79.69% <ø> (ø)
spanner-live-reverse-replication	77.42% <ø> (ø)
spanner-bulk-migration	88.21% <ø> (ø)
see 6 files with indirect coverage changes

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[derrickaw]

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