Including "canUsePlaceholder" property in worker.config

[kshyju]

Part of #1951 fix

Including canUsePlaceholder property in worker.config. This property will be used by native placeholder to determine whether the function app payload uses a new version of worker package or not.

We will be publishing a new version with this change and update our docs suggesting customers to use this version as the minimum version to get placeholder support.

Native placeholder changes to read this property is in #1955

Pull request checklist

• My changes do not require documentation changes - I will work with @mattchenderson to update the docs once our changes are out and validated.
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Additional PR information

[surgupta-msft]

Would be good to have a documentation issue created and linked for tracking. Also, any plans to add details about these changes (in host and worker) in engineering docs?

[kshyju]

Would be good to have a documentation issue created and linked for tracking. Also, any plans to add details about these changes (in host and worker) in engineering docs?

For this specific change, there won't be docs update as this is not something customers needs to be aware of. No plans to update eng docs for the related host change at this point. but may consider including this in the placeholder wiki thing I am planning.