Set max Postgres DB Connections

[badgersrus]

Why this change is needed

The dev host node errored late last night:

CRIT [04-11|21:36:08.096] failed to add batch to L2 repo           node_id=0xd6bCf7694fc4Ed7c7C61B3fC5757919E237D0bf5 component=host enclave_id=0x281330F7a477e1e525687b092089480cC1041BF7 batch=0x8ee70adf010b2dee3cee5378d96464a964f6fea10fac715d248d3f4eaf498651 err="could not add batch: failed to begin host db transaction. Cause: pq: remaining connection slots are reserved for roles with privileges of the \"pg_use_reserved_connections\" role"

What changes were made as part of this PR

• Set max connections to 100 same as edgelessDB
• (unrelated) Add check to in-mem test for batchByTx to catch any flakeyness

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[badgersrus]

I'll deploy this branch to dev first to make sure it fixes the issue

[tudor-malene]

lgtm