Allow env var with no name in dashboard

[JamesNK]

Description

The dashboard was crashing because a user had an env var on their machine with no name.

This PR changes the dashboard to allow env var with no name in dashboard. Not ideal, but better than crashing, or losing data.

Fixes #5309

Can reproduce empty env var via:

builder.AddProject<Projects.MyFrontend>("frontend")
       .WithExternalHttpEndpoints()
       .WithReference(basketService)
       .WithReference(catalogService)
       .WithEnvironment(c =>
       {
           c.EnvironmentVariables[""] = "hi";
       });

Note that resource is created by DCP but fails to start. I'm going to create a follow up issue to validate env vars set by the model always have a key. That way the host fails with a good error message before the DCP or dashboard start. Note that still doesn't stop an empty name env var from the OS.

Update: #5324

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
    • Link to aspire-docs issue:
  • No