Add foundation provider infrastructure for data and compute providers

[punit-naik-amp]

This PR establishes the base provider architecture for accessing data from different platforms and running Stitch jobs on different compute backends.

Changes:

• Add DataProvider protocol defining the interface for data sources
• Add DatabricksProviderAdapter stub (implementation in PR 2)
• Add RedshiftProviderAdapter stub with required AWS credentials, IAM role, and EMR cluster ID (implementation in PR 2)
• Add DataProviderFactory for creating data providers
• Add ComputeProvider protocol defining the interface for compute backends
• Add DatabricksComputeProvider stub (implementation in PR 3)
• Add EMRComputeProvider stub (implementation in PR 4)
• Add ProviderFactory with unified interface for both provider types
• Add comprehensive unit tests (52 tests, all passing)

Key design decisions:

• Data providers handle storage operations (no separate abstraction)
• EMR uses boto3 credential discovery (aws_profile, IAM roles, env vars)
• RedshiftProviderAdapter requires AWS credentials and accepts redshift_iam_role for COPY/UNLOAD operations
• ComputeProvider.prepare_stitch_job() receives data_provider parameter
• Pure additive changes (no modifications to existing code)

Jira: CHUCK-10

These is just the scaffolding/additive changes. No code is modified. Doing it in stages so that reviewing becomes easy. Will fold in the actual implementation of databricks and redshift in later PRs.

[punit-naik-amp]

@pragyan-amp Changed the base branch from main to CHUCK-10-redshift so that the main branch can stay clean while we merge a bunch of reviewed and tested PRs in stages to the CHUCK-10-redshift branch (as this feature involves a lot of code changes which can't be reviewed easily in one single and huge PR). In the end I will create one final PR from CHUCK-10-redshift to main.

[pragyan-amp]

Looks Good..