feat(resharding): add validation step for schema_sync

[meskill]

Add a new PostDataValidation phase for schema_sync that allows to run the validation after copying the data. Previously in #1540 the FK constraints where added with NOT VALID option marking the flag convalidated = false for the related table, which disables the check on creation for existing data and maybe disables some optimization that could be done by db for this table.

New step runs VALIDATE CONSTRAINT on this FK to make sure the convalidated is set to true on table and the db actually will start to think the values are validated. Like this since it should not block the table from actual writes comparing with creating the FK without options, so we can run this in parallel to our replication process.

The check is manual for now and later PRs will use them to run during validation.

For the remainder of the flow:

• we copy tables with COPY command
• we create FK constraints with NOT VALID since the copied data could be not in sync because different tables were copied at different snapshot time
• we replicate changes - eventually, data "should" become synchronized and valid
• the PostDataValidation could be run after the replication or after some time during the replication to see if there any errors.

[codecov]

Codecov Report

❌ Patch coverage is 99.18033% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/cli.rs	98.21%	1 Missing ⚠️

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[levkk]

Nice!