Feat/integrate connections toml

[zanebclark]

Support configuration via a connections.toml file.

Previously, credential and required argument logic was distributed across different classes and didn't consider a connections.toml file. This pull request combines configuration and credential logic, supporting an easy-to-follow order of preference for different sources. The get_merged_config function pulls from the following sources with descending preference:

1. environment variables
2. cli arguments
3. schemachange-yaml
4. connections.toml

The check_for_required_args logic is authentication-method specific.

The following cli arguments have been added:

1. --config-file-name
2. --snowflake-authenticator
3. --snowflake-private-key-path
4. --snowflake-token-path
5. --connections-file-path
6. --connection-name

Limitions / Concerns

• The snowflake cli only supports a config.toml and the Snowflake Python connector only supports a connections.toml. There's a real lack of parity across the tools here.
• Some of the connections.toml arguments use hyphens and some use underscores.
• I've been unable to find documentation on all available connections.toml options. Instead, I'll find references to specific options in different tool docs. This PR might not support all options
• I think the Snowflake Python connector and the Snowflake CLI support connection-specific environment variable overrides. I didn't implement this support in this pull request.
• The readme could use an update with the new arguments and authentication options.

[zanebclark]

@sfc-gh-tmathew and @sfc-gh-jhansen, flagging a few 4.0.0 candidates. I'm especially interested in this one, as it both simplifies the implementation and supports connections.toml configuration.

[afeld]

Wow, very impressed at the amount of work here. I'm not a schemachange maintainer, but would benefit from this. Left some suggestions.

Also, I haven't spent a lot of time in the code of the Python Connector, but it seems like schemachange is doing a lot of work around the config and connection that should be handled by the Connector. I wonder if there are ways to lean on it more heavily, allowing a lot of this schemachange code to be cut out.

Thanks, hoping this gets merged sooner or later!

[afeld]

This class and methods are pretty huge; you might consider refactoring to sub-classes for the different types of configuration to split up the logic. That could certainly be a follow-up pull request, to keep this one from getting more complex.

[afeld]

This has a lot of overlap with DeployConfig's get_session_kwargs(), so wondering if it makes sense to centralize the logic. If that doesn't make sense, would at least suggest moving it to a standalone function.

[afeld]

I suggest moving these factory() calls to fixtures to make the tests simpler.

[zanebclark]

Also, I haven't spent a lot of time in the code of the Python Connector, but it seems like schemachange is doing a lot of work around the config and connection that should be handled by the Connector. I wonder if there are ways to lean on it more heavily, allowing a lot of this schemachange code to be cut out.

@afeld, that's a great point. I maintained some legacy "check for required arguments" logic, but we could forego this and pass snowflake-related arguments to the Python Connector.