[Microbatch] Leverage static partitioning in dbt-bigquery materialization strategy

[MichelleArk]

In #1334, we introduced the microbatch strategy which leverages the dynamic partition insert/overwrite mechanism.

However, static partitioning would be significantly more performant. Benchmarking here:
https://discourse.getdbt.com/t/benchmarking-incremental-strategies-on-bigquery/981

Let's:

• Leverage static partitioning by setting partitions prior to calling the insert_overwrite_sql as part of the microbatch strategy
• Build partitions using GENERATE_TIMESTAMP_ARRAY (for 'hour' batch_size) or GENERATE_DATE_ARRAY (for all others) + __dbt_internal_microbatch_event_time_start and __dbt_internal_microbatch_event_time_end jinja context vars.