Handle TEXT data type in the backend.

[kgodey]

This issue is to ensure that Mathesar can handle the Postgres TEXT data type.

As part of this issue, we need to ensure that:

• Users can use the API to change a column to TEXT if it's possible to do so.

Additional Context

• See PR Extend the v0/databases/'s types list to show both Mathesar and DB type information. #368 for code that calculates which types are allowed for a column.
• Nothing is needed for type inference since VARCHAR covers the same use: Handle VARCHAR data type in the backend. #404