Agent templates: e2e tests + remove unnecessary app.yaml files

[bbqiu]

review the last commit only

stacked on top of #131

• remove app.yaml when unnecessary (transfer to databricks.yml file)
• NEED to keep app.yaml for templates that can be created through the UI (the UI install doesn't run databricks bundle commands)
• update relevant skills
• added + ran e2e tests (all passed in the https://db-ml-models-dev-us-west.cloud.databricks.com workspace)

All 7 templates passed (local + deploy), completed in 6 minutes 2 seconds.

  ┌───────────────────────────────────────────┬────────┐
  │                 Template                  │ Result │
  ├───────────────────────────────────────────┼────────┤
  │ agent-langgraph                           │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-langgraph-short-term-memory         │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-langgraph-long-term-memory          │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-openai-agents-sdk                   │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-openai-agents-sdk-short-term-memory │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-openai-agents-sdk-multiagent        │ PASSED │
  ├───────────────────────────────────────────┼────────┤
  │ agent-non-conversational                  │ PASSED │
  └───────────────────────────────────────────┴────────┘

[dhruv0811]

Thanks for adding testing on these templates! Will make our own devex much better for sure :)

Left a few comments on how we can make the test infra a bit lighter. Also some other minor nits and clarifications.

I tried running the tests locally, apart perm errors on lakebase and genie resources, everything passed!