Add function to get a list of integrations from a Connect server

[toph-allen]

Currently the recipe Finding Integrations uses client$GET().

Add a function get_integrations(client). It should return a list of integrations.

The Metrics Usage Dashboard in connect-extensions uses this functionality, added in posit-dev/connect-extensions#128.

[toph-allen]

The Metrics Usage Dashboard in connect-extensions uses this functionality, added in posit-dev/connect-extensions#128.