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ARROW-4313: Define general benchmark database schema

This is a work in progress. It provides the ddl for a proposed schema for the benchmark database.

- The Dockerfile loads the ddl into the appropriate directory so that it will be added upon startup.
- The `examples` directory will probably be deleted before this is completed. Some of the queries do not work (was surprised that 'null' does not compare to equal).
- My SQL style may be ugly (depending on preference) so it can change; no problem.

Thank you for this opportunity to learn!

Author: Tanya Schlusser <tanya@tickel.net>

Closes #3586 from tanyaschlusser/ARROW-4313 and squashes the following commits:

25e0b76ef <Tanya Schlusser> ARROW-4313: Ingestion functions moved out of the trigger functions file; redundant permissions revocation removed
d47b1e57d <Tanya Schlusser> ARROW-4313: Add 'summarized_tables_view' to the views file; improve documentation functions; re-push generated documentation files.
e5ce80ae0 <Tanya Schlusser> ARROW-4313: Add ingestion function 'ingest_benchmark_runs_with_context' and example
72132ccf6 <Tanya Schlusser> ARROW-4313: Standard JSON (not strings) is acceptable for field entries
3fa5f3a74 <Tanya Schlusser> ARROW-4313: Add license to '.env'
7637cac36 <Tanya Schlusser> ARROW-4313: allow Travis to skip .csv files
7e0ef1d2a <Tanya Schlusser> ARROW-4313: Add a benchmarking database schema