Add rename_constraint operation

[SferaDev]

In the frontend when renaming a column we were adding OpRawSQL operations that ALTER TABLE "${tableName}" RENAME CONSTRAINT "${oldName}" TO "${newName}"; to keep the constraints up to date for the data api to like them. Proposing to expose a new operation for that use case.

Before merging, an example should be added for the new operation.

[andrew-farries]

Looks good 👍 Thanks for doing it 🙏

We also need:

• An example migration in /examples . Either add a migration to create a table with a constraint then another migration to rename it, or just add a migration to rename one of the constraints created in an existing example.
• Update the docs/README.md file operations reference section.

[andrew-farries]

I think the example can be:

{
  "name": "33_rename_check_constraint",
  "operations": [
    {
      "rename_constraint": {
        "table": "people",
        "from": "name_length",
        "to": "name_length_check"
      }
    }
  ]
}

to rename one of the constraints created by an earlier migration.