Backport VReplication: Support reversing read-only traffic in vtctldclient (#16920)

[mhamza15]

Backports vitessio#16918

PR Overview

This PR backports changes from a recent Vitess issue to add support for reversing read‐only traffic in the vtctldclient. Key changes include updates to workflow test logic for both read and write switching, enhanced logging and tracing in the vtctldclient and server components, and adjustments to routing rules and tablet type handling to support the reverse operation.

Reviewed Changes

File	Description
go/test/endtoend/vreplication/resharding_workflows_v2_test.go	Adjusted test functions and parameter names to improve clarity for reads.
go/test/endtoend/vreplication/vreplication_vtctldclient_cli_test.go	Added additional nil checks and refinement of tablet type usage in tests.
go/vt/vtctl/workflow/server.go	Integrated tracing and refined traffic switching logic with enhanced logging.
go/test/endtoend/vreplication/wrappers_test.go	Updated vtctld workflow command execution with improved logging.
go/test/endtoend/vreplication/movetables_buffering_test.go	Modified global tablet configuration for buffering tests with proper deferral.
go/vt/vtctl/workflow/traffic_switcher.go	Enhanced logging in switchShardReads and switchTableReads for better diagnostics.
go/test/endtoend/vreplication/config_test.go	Added new materialization spec definitions for extended test coverage.
go/test/endtoend/vreplication/helper_test.go	Improved error reporting by including routing rules in tablet query assertions.

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Comments suppressed due to low confidence (3)

go/test/endtoend/vreplication/resharding_workflows_v2_test.go:330

• Renaming the parameter from 'tabletTypes' to 'tabletType' improves clarity by indicating that a single tablet type is expected. Please verify that all call sites pass the intended value.

func validateReadsRoute(t *testing.T, tabletType string, tablet *cluster.VttabletProcess) {

go/test/endtoend/vreplication/movetables_buffering_test.go:21

• Modifying global variables 'defaultRdonly' and 'defaultReplicas' in this test may affect test isolation. Ensure that the deferred restoration consistently resets these values to avoid interference across tests.

defaultRdonly = 0
	defaultReplicas = 0

go/vt/vtctl/workflow/traffic_switcher.go:550

• [nitpick] The enhanced logging here provides detailed workflow, direction, and tablet type information for debugging. Please verify that including these details in logs is acceptable in production environments and does not expose sensitive data.

ts.Logger().Infof("switchShardReads: workflow: %s, direction: %s, cells: %v, tablet types: %v", ts.workflow, direction.String(), cells, servedTypes)

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