Add setup for DBR testing

[shreyas-goenka]

Changes

This PR adds a notebook we can use to easily run and iterate on DBR tests.

Why

Simplifies the test setup and makes it easy to debug issues with the DBR testing framework itself. You just have to run make dbr_scratch to get started.

[eng-dev-ecosystem-bot]

Run: 18380840675

	Env	🔄​flaky	✅​pass	🙈​skip
🔄​	aws linux	1	323	544
✅​	aws windows		325	543
🔄​	aws-ucws linux	9	431	440
🔄​	aws-ucws windows	9	432	439
✅​	azure linux		324	543
✅​	azure windows		325	542
🔄​	azure-ucws linux	9	431	439
🔄​	azure-ucws windows	9	432	438
🔄​	gcp linux	1	322	545
✅​	gcp windows		324	544

14 failing tests:

Test Name	aws linux	aws-ucws linux	aws-ucws windows	azure-ucws linux	azure-ucws windows	gcp linux
TestAccept/bundle/deploy/dashboard/detect-change	✅​p	🔄​f	🔄​f	🔄​f	✅​p	✅​p
TestAccept/bundle/deploy/dashboard/generate_inplace	✅​p	🔄​f	🔄​f	🔄​f	🔄​f	✅​p
TestAccept/bundle/deploy/dashboard/nested-folders	✅​p	🔄​f	🔄​f	🔄​f	✅​p	✅​p
TestAccept/bundle/deploy/dashboard/simple	✅​p	🔄​f	🔄​f	🔄​f	🔄​f	✅​p
TestAccept/bundle/deploy/dashboard/simple_outside_bundle_root	✅​p	🔄​f	🔄​f	🔄​f	🔄​f	✅​p
TestAccept/bundle/deploy/dashboard/simple_syncroot	✅​p	🔄​f	🔄​f	🔄​f	🔄​f	✅​p
TestAccept/bundle/deploy/registered_models/basic	🙈​s	✅​p	✅​p	✅​p	🔄​f	🙈​s
TestAccept/bundle/deploy/registered_models/basic/DATABRICKS_BUNDLE_ENGINE=direct-exp		✅​p	✅​p	✅​p	🔄​f
TestAccept/bundle/deployment/bind/dashboard	✅​p	🔄​f	🔄​f	🔄​f	✅​p	✅​p
TestAccept/bundle/deployment/bind/dashboard/recreation	✅​p	🔄​f	🔄​f	🔄​f	✅​p	✅​p
TestSetupDbrRunner	🔄​f	✅​p	✅​p	✅​p	✅​p	🔄​f
TestDashboardAssumptions_WorkspaceImport	✅​p	🔄​f	🔄​f	🔄​f	🔄​f	✅​p
TestFilerWorkspaceNotebook	✅​p	✅​p	✅​p	✅​p	🔄​f	✅​p
TestFilerWorkspaceNotebook/rNb.r	✅​p	✅​p	✅​p	✅​p	🔄​f	✅​p