store: Embed contract source in dynamic data source

For now, we write the source for a dds into two places redundantly. In
future changes, we will copy existing data into the new attributes and
start reading from there. Since the copying is very slow on the hosted
service, we split the migration into the new schema up into multiple steps.

store: Fix build error

A bad rebase in commit cd85fd0 broke compilation of a test

node: Add a command to inspect database pool sizes

graphql: Add `subgraphError` argument only when feature is present

We saw an issue in a graphql client that is avoided by doing this.
and it is generally more correct to only include it if the subgraph opts in.
This requires storing the `features` field in the metadata, which we should be doing anyways.