Compact PG DB migration scripts into a single step before v1.0 substrate release

In https://github.com/agent-substrate/substrate/pull/1196#discussion_r3890774469 we agreed to group all pre-v1 DB migration operations into a single migration step.

Doing this will minimize startup time cost for new clusters. If we don't do it, the startup code for new clusters will be slower ~forever (unless we get really creative in how we manage migration scripts, which is not planned, and which caries it's own risks).

We should do this just prior to releasing v1 since we anticipate that additional DB migration scripts will be added between now and then.

@juli4n @iplay88keys @BenTheElder @thockin