Create new columns in table user_saved_search

[chouinar]

To the DB we want to make the following two changes. Add a last_modified_at column like so:

last_notified_at: Mapped[datetime] = mapped_column(
        nullable=False,
        default=datetime_util.utcnow,
        server_default=sqlnow(),
    )

Also add an int array column for opportunity IDs to be stored (this doesn't need to be any sort of foreign key), call this searched_opportunity_ids

Acceptance criteria

• DB table updated to include two new columns
• Factories created/updated

[babebe]

Split this work into 2 different tickets

Summary

We want to:

• Modify the users query to replace the pagination with exactly{"order_by": "post_date", "page_offset": 1, "page_size": 1000, "sort_direction": "descending"}

• Query the search index with this query, limiting the results to only opportunity ID

• Store the list of opportunity IDs returned to the DB as a list/array (does not need to point to opportunity table as foreign keys)

We want to change the users query so that we have a relatively consistent set of results and don't have to factor in whatever they were sorting by / how much they were limiting / page number. Effectively we want the 1000 most recent results.

We'll later use this information in a backend job to determine changed search queries