feat: add function_runtime to the manifest

[srajiang]

Type of change (place an x in the [ ] that applies)

• [ ] New sample
• [ ] New feature
• [ ] Bug fix
• [ ] Documentation
• [x] Other

Summary

function_runtime will shortly be a required property when an app manifest contains functions. Setting this to remote which should be set for all non ROSI hosting scenarios.

Requirements (place an x in each [ ] that applies)

• [x] I’ve checked my submission against the Samples Checklist to ensure it complies with all standards
• [x] I have ensured the changes I am contributing align with existing patterns and have tested and linted my code
• [x] I've read and agree to the Code of Conduct