…s to staging tables

…s to staging tables (#1894)

## Summary
Part of #1686 (separate for easier review)

### Time to review: __2 mins__

## Changes proposed
- Add `created_at`, `updated_at`, and `deleted_at` columns to staging
tables
- Better logging of migrate queries

## Context for reviewers
These columns will provide helpful metadata for understanding or
troubleshooting the load process.

The `created_at` and `updated_at` columns are set automatically by
SQLAlchemy.

For `deleted_at`, I will update #1852 after this is merged.

## Additional information
Example from local testing:
![Screenshot 2024-05-01 at 11 31
47](https://github.com/HHS/simpler-grants-gov/assets/3811269/e9513de8-ceff-42c9-bccc-d2fcfc5fe7bf)

…#1852)

## Summary
Fixes #1686

## Changes proposed
- Add class `LoadOracleDataTask` which loops through each legacy table
and loads the data into the corresponding staging table.
- Add a module of functions `src.data_migration.load.sql` to generate
sqlalchemy SQL expressions for the loads.
- Add a script `seed_local_legacy_tables.py` to generate fake data in
the local legacy tables.
- Add unit tests.

## Context for reviewers
This is a new batch task which loads data from the legacy (Oracle)
tables to staging tables.

It is incremental and handles the following situations:

| Situation | Detection logic | Action |
| ------------- | ------------- | ------------- |
| New row in source table | Primary key not present in destination table
| Insert into destination, set `transformed_at=NULL` |
| Updated row in source | Primary key exists in both source &
destination AND newer `last_upd_date` | Update in destination, reset
`transformed_at=NULL` |
| Deleted row in source | Primary key does not exist in source, AND not
`is_deleted` in destination | Set `is_deleted=TRUE`, reset
`transformed_at=NULL`
| Unchanged | Primary key exists in both source & destination AND
`last_upd_date` is not newer | No write to destination |

## Additional information
To run the code locally with fake data:

```
make setup-foreign-tables  # once
make seed-local-legacy-tables  # repeat to add & update data
poetry run python3 -m src.data_migration.load.load_oracle_data_task
```