SNOW-1569916: fix local testing default timestamp timezone issue

[sfc-gh-aling]

1. Which Jira issue is this PR addressing? Make sure that there is an accompanying issue to your PR.

   Fixes SNOW-1569916

2. Fill out the following pre-review checklist:

   • I am adding a new automated test(s) to verify correctness of my new code
     • If this test skips Local Testing mode, I'm requesting review from @snowflakedb/local-testing
   • I am adding new logging messages
   • I am adding a new telemetry message
   • I am adding new credentials
   • I am adding a new dependency
   • If this is a new feature/behavior, I'm adding the Local Testing parity changes.

3. Please describe how your code solves the related issue.

in snowflake, the default timestamp type is controlled by the session parameter TIMESTAMP_TYPE_MAPPING:
https://docs.snowflake.com/en/sql-reference/parameters#label-timestamp-type-mapping

in local testing, we didn't have this testing, leaving the default timestamp type timezone information is empty.
this leads to incorrect behavior when users are using convert_timezone method.

this PR introduces a private module variable TIMESTAMP_TYPE_MAPPING as a temporary workaround to align with the default snowflake behavior -- when to_timestamp is called, the timestamp should have timezone type being NTZ.

this PR also added coercion for default timezone type and NTZ timezone type.