Add a trigger for updated_on in the catalog database

[AetherUnbound]

Problem

Unless explicitly set, the updated_on column for the primary media tables in the catalog is modified when a record is updated via ingestion, but is not modified when any other update (e.g. a `batched_update) is performed. This can create situations where a record is inaccurately assumed to have not been updated even it has been by some other process.

Description

We should add a trigger for the following columns which automatically sets the value to the current timestamp:

openverse/docker/upstream_db/0003_openledger_image_schema.sql

Line 19 in 4798866

updated_on timestamp with time zone NOT NULL,

openverse/docker/upstream_db/0006_openledger_audio_schema.sql

Line 20 in 4798866

updated_on timestamp with time zone NOT NULL,

This can be done using the moddatetime extension (which I've verified is available on the catalog database). Here's an example from StackExchange for how it might look:

CREATE EXTENSION moddatetime;

CREATE TRIGGER mdt_image
  BEFORE UPDATE ON image
  FOR EACH ROW
  EXECUTE PROCEDURE moddatetime (updated_on);

The documntation for the updated_on column will also need to be updated with this change:

openverse/catalog/utilities/media_props_gen/docs/media_props.md

Lines 23 to 30 in efc2a0b

	# updated_on
	## Description
	The timestamp of the last time any change was made to the media item. Unlike
	`last_synced_with_source`, this can also be a change from a data cleaning step,
	e.g. updating license URL in the `meta_data`, or fixing the URL using the
	`batched_update` DAG.

Note

Once this is added, we'll need to remove the code that explicitly sets the updated_on column.
This may involve changes to the following areas:

• TimestampColumn update strategy definition
• Batched update parameters
• Popularity update

Alternatives

We could rely on adding a step to update updated_on for every source of updates (see #4460 as an example). This would require more maintenance and touch points than modifying the tables themselves to perform this update for us.

Additional context

This has been discussed a few previous times, see: #4460, #4366 (comment), #4429 (comment).