agent,common: Migrate subgraph deployment assignments to use explicit 'paused' mechanism

[fordN]

Graph-node recently added support for explicit pausing of subgraph deployments (in the past they were paused virtually by assigning the deployment to a nonexistent node).

This PR adds a migration that interacts with the Graph Node indexingStatuses query and JSON-RPC server to update all virtually paused deployments (node = 'removed') to use the new explicit pausing mechanism.