[vtctld] migrate validator rpcs

[ajm188]

Description

This PR migrates the Validate and Validate{Keyspace, Shard} rpcs to the new VtctldServer.

Examples

❯ vtctldclient --server ":15999" Validate
Validation complete; no issues found.
❯ vtctldclient --server ":15999" ValidateKeyspace commerce
Validation of commerce complete; no issues found.
❯ vtctldclient --server ":15999" ValidateShard commerce/0
Validation of commerce/0 complete; no issues found.
❯ vtctldclient --server ":15999" ValidateShard commerce/0 -p
Validation of commerce/0 complete; no issues found.
❯ ps aux | grep vttablet | grep -v grep | shuf -n 1
amason           47526   0.0  0.2  5055136  75312 s000  S     6:46AM   0:00.37 vttablet -topo_implementation etcd2 -topo_global_server_address localhost:2379 -topo_global_root /vitess/global -log_dir /Users/amason/work/vitess/vtdataroot/tmp -log_queries_to_file /Users/amason/work/vitess/vtdataroot/tmp/vttablet_0000000101_querylog.txt -tablet-path zone1-0000000101 -tablet_hostname  -init_keyspace commerce -init_shard 0 -init_tablet_type replica -health_check_interval 5s -enable_semi_sync -enable_replication_reporter -backup_storage_implementation file -file_backup_storage_root /Users/amason/work/vitess/vtdataroot/backups -restore_from_backup -port 15101 -grpc_port 16101 -service_map grpc-queryservice,grpc-tabletmanager,grpc-updatestream -pid_file /Users/amason/work/vitess/vtdataroot/vt_0000000101/vttablet.pid -vtctld_addr http://SFO-M-AMASON02:15000/
❯ kill -9 47526
❯ vtctldclient --server ":15999" ValidateShard commerce/0 -p
Validation results:
- Ping(zone1-0000000101) failed: rpc error: code = DeadlineExceeded desc = latest balancer error: connection error: desc = "transport: Error while dialing dial tcp [::1]:16101: connect: connection refused" tablet hostname: localhost
E0923 06:48:01.531351   48260 main.go:42] shard commerce/0 had validation issues; see above for details
❯ vtctldclient --server ":15999" Validate -p
Validation results:

For commerce:

For commerce/0:
- Ping(zone1-0000000101) failed: rpc error: code = DeadlineExceeded desc = latest balancer error: connection error: desc = "transport: Error while dialing dial tcp [::1]:16101: connect: connection refused" tablet hostname: localhost
E0923 06:48:46.939330   48287 main.go:42] some issues were found during validation; see above for details

Related Issue(s)

Closes #8847
Closes #8848

Checklist

• Should this PR be backported? - No
• Tests were added or are not required
• Documentation was added or is not required

Deployment Notes

[ajm188]

unit tests and cli entrypoints to come tomorrowwwww

[ajm188]

just calling out deviations inline; this one was not a pure porting of behavior because I saw some things that could be improved

[ajm188]

One change to the implementation is I bounded all the remote calls (both to the topo and to tablet tmc calls) with timeouts. If I didn't do this, I could kill a tablet, and the Validate call would hang until action_timeout, which defaults to 24 hours.

[ajm188]

Another deviation from the original implementation: we used to make a call to GetKeyspaces in the outer function, and then the first thing this goroutine would do is ....... also make a call to GetKeyspaces, so, I just removed it and used the earlier result.

[deepthi]

LGTM