feat(Postgres Node): Add option IS NOT NULL and hide value input fields

[ayatnkw]

Summary

• Add IS NOT NULL operator in options for Postgres and MySql
• Hide value input field for options IS NULL and IS NOT NULL as no values should be assigned

Related tickets and issues

Community: Postgres Is Null condition should honor false for Is Not Null

Review / Merge checklist

• [ ] PR title and summary are descriptive. Remember, the title automatically goes into the changelog. Use (no-changelog) otherwise. (conventions)
• [ ] Docs updated or follow-up ticket created.
• [ ] Tests included.

  A bug is not considered fixed, unless a test is added to prevent it from happening again. A feature is not complete without tests.