VTAdmin: Add support for Create Reshard

[beingnoble03]

Description

This PR adds support to create a reshard workflow directly from VTAdmin. Contains both API and Web changes.

Related Issue(s)

• VTAdmin: Enhance VReplication functionality in vtadmin UI #11690

Screenshots

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

Deployment Notes

[vitess-bot]

Review Checklist

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• Protobuf changes should be wire-compatible.
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[codecov]

Codecov Report

Attention: Patch coverage is 4.00000% with 24 lines in your changes missing coverage. Please review.

Project coverage is 69.40%. Comparing base (f40e076) to head (de272c9).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtadmin/http/workflows.go	0.00%	14 Missing ⚠️
go/vt/vtadmin/api.go	9.09%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16903      +/-   ##
==========================================
- Coverage   69.43%   69.40%   -0.03%     
==========================================
  Files        1570     1570              
  Lines      203812   203871      +59     
==========================================
- Hits       141517   141499      -18     
- Misses      62295    62372      +77     

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[rohit-nayak-ps]

In the UI

• Move source shards to row below so the shards are next to each other
• Change label "Source Keyspace" => "Keyspace" since there is just one keyspace

Rest looks good

[beingnoble03]

In the UI

• Move source shards to row below so the shards are next to each other
• Change label "Source Keyspace" => "Keyspace" since there is just one keyspace

Rest looks good

Done.

[mattlord]

Looks good! I tested it locally on the PR branch with:

make build
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; ./204_switch_writes.sh; ./205_clean_commerce.sh; ./301_customer_sharded.sh; ./302_new_shards.sh

Then in VTAdmin creating a Reshard workflow from the 0 shard to the -80,80- shards (what the ./303_reshard.sh script does).

Thanks! ❤️