Add required 'begin' config for testing microbatch models

[MichelleArk]

resolves #dbt-labs/dbt-adapters#315, but for dbt-snowflake
docs dbt-labs/docs.getdbt.com/#

Problem

dbt-core is adding a required config, named begin for microbatch models in dbt-labs/dbt-core#10756.

Solution

Add begin config ahead of time!

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX

[github-actions]

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