[Feature] Added `databricks_functions` data source

[alexott]

Changes

It's now possible to fetch information about functions defined in a specific UC schema.

No integration test yet because we don't have databricks_function resource yet.

Resolves #4111

Tests

• [x] make test run locally
• [x] relevant change in docs/ folder
• [ ] covered with integration tests in internal/acceptance
• [ ] relevant acceptance tests are passing
• [x] using Go SDK

[eng-dev-ecosystem-bot]

Test Details: go/deco-tests/11594169997