Implement tabular entity handlers inheriting data from DBI

[eblondel]

The purpose is to have entity tabular handlers (based on the simplified geoflow entity pivot model) from which we can inherit the data part from the database. A similar approach was followed in the past for entities that are described from a table, but that are enriched with Thredds data source.

A main entity tabular handler will be set as handle_entities_dbi_df, then recycled for handlers specific to access formats dbi, csv, excel, gsheet.

The enrichment will be operated if a DB table is found with same name as the entity id, if not it will be simply skipped.

Development sponsored by IRD @IRDnamik @kikislater @juldebar

[eblondel]

@juldebar New entity handlers have been added: dbi_csv, dbi_excel, dbi_gsheet. The dbi handler (assuming a dcmi metadata table in the DB) also inherit from this behavior where the data part will be auto created from the DBI.