Add function to index observation text from existing observations saved in SQLite db

[JWCook]

Currently this is done by calling index_observation_text() with Observation objects.

For cases where observations are already stored in SQLite, it would be faster to have an option to do this directly with SQL.

[JWCook]

Update: It seems that the current table format would require using the json_each() function to accomplish this, which requires SQLite 3.38+. So options for this would be:

1. Use separate tables instead of denormalized JSON fields for observation identifications, comments, OFVs, annotations, and tags.
2. Require manually installing SQLite (or for naturtag, package SQLite binaries with it)