Enable specifying install search location options for published apphost

[elinor-fung]

See https://github.com/dotnet/designs/blob/main/proposed/apphost-embed-install-location.md.

dotnet/runtime#104749 enabled embedding install location options in apphost. This is the SDK side to use that ability.

• AppHostDotNetSearch allows selection of which search locations should be used
  • Errors on creating apphost if set to an invalid value
• AppHostRelativeDotNet allows specifying a relative path to the runtime
  • Setting implies AppHostDotNetSearch=AppRelative if AppHostDotNetSearch is not explicitly set
• Values are only embedded in apphost on publish (not build)

cc @dotnet/appmodel @AaronRobinsonMSFT

[richlander]

Can you update the spec to clarify if ../ style relative paths are supported and what the behavior is? That seems important to document.

https://github.com/dotnet/designs/blob/main/proposed/apphost-embed-install-location.md#app-relative-path-to-install-location

For a relative location, is the guidance to (for example) explode a runtime tarball at a .dotnet directory? I'm asking about the intended deployment side.

[elinor-fung]

Can you update the spec to clarify if ../ style relative paths are supported and what the behavior is? That seems important to document.

https://github.com/dotnet/designs/blob/main/proposed/apphost-embed-install-location.md#app-relative-path-to-install-location

dotnet/designs#319

For a relative location, is the guidance to (for example) explode a runtime tarball at a .dotnet directory? I'm asking about the intended deployment side.

That is probably the simplest option. I kind of intentionally didn't include an explicit/official recommendation and left the deployment side as a 'it is up to the developer to create the install layout' - until we sort out an SDK experience.

[vitek-karas]

Looks good - thanks!