INSERTs having Cross shard foreign keys support

[GuptaManan100]

Description

This PR adds support for planning DML queries that require a foreign key value to exist on the parent table.

Related Issue(s)

• RFC: Foreign Key Support in Vitess #12967

Checklist

• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI

[vitess-bot]

Review Checklist

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[GuptaManan100]

Closing since this work is deferred for now.