Updates SnowflakeCredentials to implement the CredentialsBlock abstract block type

[desertaxle]

Adds a get_client method to SnowflakeCredentials and refactors interaction with SnowflakeConnector so that SnowflakeCredentials now owns creation of SnowflakeConnection instances.

Example

Get Snowflake connection with only block configuration:

from prefect_snowflake import SnowflakeCredentials
snowflake_credentials_block = SnowflakeCredentials.load("BLOCK_NAME")
connection = snowflake_credentials_block.get_client()

Get Snowflake connector scoped to a specified database:

from prefect_snowflake import SnowflakeCredentials
snowflake_credentials_block = SnowflakeCredentials.load("BLOCK_NAME")
connection = snowflake_credentials_block.get_client(database="my_database")

Screenshots

Docs for new get_client method.

Checklist

• References any related issue by including "Closes #" or "Closes ".
  • If no issue exists and your change is not a small fix, please create an issue first.
• Includes tests or only affects documentation.
• Passes pre-commit checks.
  • Run pre-commit install && pre-commit run --all locally for formatting and linting.
• Includes screenshots of documentation updates.
  • Run mkdocs serve view documentation locally.
• Summarizes PR's changes in CHANGELOG.md

[ahuang11]

Minor comments, but looks good!

[ahuang11]

Thanks!