VReplication: Support reversing read-only traffic in vtctldclient

[mattlord]

Description

This PR fixes a bug in vtctldclient, in that it did not support a needed feature that the legacy vtctlclient did (see the client transition docs). Specifically, support for using ReverseTraffic when traffic for read-only tablet types (REPLICA, RDONLY) have been switched BUT writes (PRIMARY tablet type) have not.

Using the manual test from below, this fails with vtctldclient but works with vtctlclient:

❯ vtctldclient MoveTables --workflow commerce2customer --target-keyspace customer reversetraffic --tablet-types "rdonly,replica"
E1009 20:59:35.000461   35915 main.go:56] rpc error: code = Unknown desc = no streams found in keyspace commerce for commerce2customer_reverse

❯ vtctlclient MoveTables -- reversetraffic customer.commerce2customer --tablet_types "rdonly,replica"
W1008 19:45:47.734875   67717 log.go:39] Failed to read in config : Config File "vtconfig" Not Found in "[/Users/matt/git/vitess/examples/local]". This is optional, and can be ignored if you are not using config files. For a detailed explanation, see https://github.com/vitessio/vitess/blob/main/doc/viper/viper.md#config-files.
reversetraffic was successful for workflow customer.commerce2customer
Start State: All Reads Switched. Writes Not Switched
Current State: Reads Not Switched. Writes Not Switched

I think that it makes sense to backport this at least to v21 and v20 so that this is addressed in a minimum of 1 GA branches/releases.

Manual test

alias vtctldclient='command vtctldclient --server=localhost:15999'
cd examples/local

./101_initial_cluster.sh; mysql < ../common/insert_commerce_data.sql; ./201_customer_tablets.sh; ./202_move_tables.sh; ./203_switch_reads.sh

echo -e "\nReversing traffic for reads..."
vtctldclient MoveTables --workflow commerce2customer --target-keyspace customer reversetraffic --tablet-types "rdonly,replica"
echo

With the client command output on the PR branch being:

Reversing traffic for reads...
ReverseTraffic was successful for workflow customer.commerce2customer

Start State: All Reads Switched. Writes Not Switched
Current State: Reads Not Switched. Writes Not Switched

Related Issue(s)

• Fixes: Feature Request: ReverseTraffic for only replica and rdonly tablet types #16918

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

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[codecov]

Codecov Report

Attention: Patch coverage is 74.28571% with 9 lines in your changes missing coverage. Please review.

Project coverage is 69.42%. Comparing base (056afc9) to head (fbd7ad6).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtctl/workflow/server.go	71.87%	9 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16920      +/-   ##
==========================================
- Coverage   69.45%   69.42%   -0.04%     
==========================================
  Files        1570     1570              
  Lines      203631   203876     +245     
==========================================
+ Hits       141441   141537      +96     
- Misses      62190    62339     +149     

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