AWS Athena Compatibility for seeds

[sah129]

Is your feature request related to a problem? Please describe.
Cannot load seed files when using AWS Athena.

Describe the solution you'd like

• Update athena__load_seed in load_seed.sql to write seed files from Tuva's s3 bucket to a temp table. Final table (written to client's s3 bucket) is created from temp table.
• Update seed column type definitions to use real or int for approximate and exact numeric data types (respectively) when target.type == 'athena'

Describe alternatives you've considered
I've explored using dbt-athena-external-tables to stage each seed file via run-operation, but ultimately it was easier to modify load_seed.sql as dbt-athena-external-tables is still experimental and not yet merged into the dbt-athena adapter. That said, dbt-external-tables looks promising for other data warehouses and could be worth looking into.

Additional context
I have this working in my environment (fork here). Going to do a little more testing/code clean-up before submitting a PR.

[aneiderhiser]

Sounds great @sah129 -- thanks for working on this!