[Internal] Set user agent in some resources implemented in plugin framework

[tanmay-db]

Changes

Following up for https://github.com/databricks/terraform-provider-databricks/pull/4161#discussion_r1822044825, I noticed some other resources also aren't setting the user agent. Creating a PR to fix them. Also added a note in the contributing guideline.

Tests

NA

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

[github-actions[bot]]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger: go/deco-tests-run/terraform

Inputs:

• PR number: 4187
• Commit SHA: c8d85adef05e47103f3058a73d98ba7d414a0f4c

Checks will be approved automatically on success.

[eng-dev-ecosystem-bot]

Test Details: go/deco-tests/11843045111