Integration Testing: Content refresh

[jkodroff]

https://www.pulumi.com/docs/iac/guides/testing/integration/

We need to break this content up and ensure the copy is up to our current style standards:

• Move the integration testing framework page to its own subpage of Integration Testing.
  • The Go examples still use v2 of the Pulumi SDK and should be upgraded to v3. Grab a simple example from the pulumi/pulumi-aws repository's tests. (Fixes Update integration testing docs for v3 #11743)
  • Grab the relevant links from Full Examples (but maybe point to pulumi/pulumi-aws as our best example), put this in Additional Resources
• Move the Automation API content to a new subpage of Integration Testing:
  • Break out the testing steps into a numbered list for readability
  • Use the Automation API example links from Full Examples under Additional Resources
  • I think this is our best existing example of Automation API in Java, but it does not show assertions: https://github.com/pulumi/automation-api-examples/blob/main/java/localProgram/README.md
• Discard the section on ephemeral environments as it's outdated.
• Move the remaining content to an Overview page:
  • Explain what integration testing is in this context and why you might want to do it
  • Explain the specific benefits of what you can guarantee into its own section
  • Explain what the supported integration testing options are:
    • Integration testing framework (link to the new page) and explain the basic benefits and language constraints (the tests have to be written in Go, supports a Pulumi program in any language).
    • Use Automation API (link to the new page) to do the CLI actions and write tests/assertions using the tooling of your choices. Explain the language constraints (it's not available in YAML).
    • You can also write integration tests by shelling out the Pulumi commands and making assertions in any language. Automation API makes this easier.