Write helper function to check for values

A lot of the ingest scripts contain similar code to look to see if values already exist in the database. (e.g., telescope, instrument, filter, etc.) I think we could use a helper function here. Something like this
```python
def in_database(db, value, table, field):
match = (
db.query(db.table)
.filter(db.table.c.field == value)
.table()
)

if len(match) == 0:
msg = f"Value {value} not found in {table} table."
return false
else
return true
```

I'm not exactly sure how to compose the pointers in the query (`f"db.{table}.c.{field}`?) but I think the answer is in here: https://docs.sqlalchemy.org/en/20/faq/sqlexpressions.html