Deprecate the V1 API

This gives a warning for using the V1 API in Juno and encourages users
to switch to V2 before the K release where it will be removed.

DocImpact
Implements blueprint deprecate-v1-api
Change-Id: I89eb9eb2a7819edb2a97b2ea2b5239a89124ca4d
Merge "Deprecate the V1 API"