Terraform template for Reverse replication for sharded MySQL

[manitgupta]

Adds a terraform template for reverse replication for sharded MySQL. Tested in VPC and non-VPC environments. Uses null_resource to create and destroy changestreams via terraform since Spanner does not expose terraform constructs to manage the lifecycle of a changestream.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 52.41%. Comparing base (cc17ed1) to head (fcf0f8e). Report is 34 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1946      +/-   ##
============================================
+ Coverage     44.72%   52.41%   +7.68%     
+ Complexity     3869     1320    -2549     
============================================
  Files           832      371     -461     
  Lines         49444    20393   -29051     
  Branches       5192     2059    -3133     
============================================
- Hits          22115    10689   -11426     
+ Misses        25683     9036   -16647     
+ Partials       1646      668     -978     

Components	Coverage Δ
spanner-templates	67.27% <ø> (+1.71%)	:arrow_up:
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	76.18% <ø> (+1.31%)	:arrow_up:
spanner-live-reverse-replication	76.54% <ø> (+0.99%)	:arrow_up:
spanner-bulk-migration	85.55% <ø> (+1.35%)	:arrow_up:

see 497 files with indirect coverage changes