Add default value support for rename_column_concurrently

What does this MR do and why?

This makes it possible to use rename_column_concurrently for columns with a default value. !52032 (merged) explains the problem in more detail.

This MR aims to implement the solution outlined in !52032 (merged):

the default is a constant value - add additional checks in the insert trigger, where we inspect incoming values. If one column is set to the default, and the other is not, we can assume the non-defaulted value is the correct value.

How to set up and validate locally

1. Check out the andysoiron/rename_column_concurrently-with-default-test-migrations branch. This includes some migrations to test the changes. You can compare the changes here.
2. Run rails db:migrate
3. The last migration is expected to fail with rename_column_concurrently does not currently support columns with default functions
4. In rails console, create a test record

   t = DefaultTest.create

5. All columns should have the default value:

   > id: 1, test_function: Fri, 05 Aug 2022 14:38:51.231085000 UTC +00:00, test_string: "test", test_integer: 1, test_string_new: "test", test_integer_new: 1

6. Update the old and new columns and reload.

   t.update(test_integer: 2, test_string_new: 'new')
   t.reload

7. All columns should now have the updated values

   > id: 1, test_function: Fri, 05 Aug 2022 14:38:51.231085000 UTC +00:00, test_string: "new", test_integer: 2, test_string_new: "new", test_integer_new: 2

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related issue: #339948 (closed)