Allow starting waiting resources

[JamesNK]

Description

Addresses #5879

Previously Waiting resources could not start until the resource they are waiting on became healthy. The resource would wait and the "Start" button was disabled.

This PR enables the resource-start custom act for waiting resources. That makes it possible to click on the "Start" button for a waiting resources to explicitly start before its dependencies are healthy.

Note that this change doesn't tell lower-level app host code that is waiting for a healthy event to stop waiting. That also needs to be done (either in this PR or a future PR) to properly clean up state when "Start" is clicked.

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Is this introducing a breaking change?
      • Yes
        • Link to aspire-docs issue (please use this breaking-change template):
      • No
        • Link to aspire-docs issue (please use this doc-idea template):
  • No

[davidfowl]

I expected a much bigger refactoring that changes the state machine to make it possible to not only stop waiting but restart and enter the waiting state again

[davidfowl]

@JamesNK is this PR still valid?

[davidfowl]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[davidfowl]

Note that this change doesn't tell lower-level app host code that is waiting for a healthy event to stop waiting. That also needs to be done (either in this PR or a future PR) to properly clean up state when "Start" is clicked.

@JamesNK do you want to treat that issue as fixed or file another one for this follow up?