node: check that at least one replica for each shard has a non-zero weight

[lutter]

No description provided.

[evaporei]

Just for future context, this is being added because an indexer bumped into this error:

thread 'tokio-runtime-worker' panicked at 'attempt to calculate the remainder with a divisor of zero', store/postgres/src/deployment_store.rs:1039:21

That happened because their config file had only one shard which the weight was 0:

[store]
[store.primary]
connection = "postgresql://${postgres_user}:${postgres_pass}@${postgres_host}:5432/${postgres_db}?host=/var/run/postgresql"
weight = 0
pool_size = 30

[chains]
ingestor = "index_node_1"

[deployment]
[[deployment.rule]]
indexers = [ "index_node_0", "index_node_1" ]

[general]
query = "query_node_0"

The error happens because the replica_order list is empty:

graph-node/store/postgres/src/deployment_store.rs

Line 1038 in 73075df

self.conn_round_robin_counter.fetch_add(1, Ordering::SeqCst) % weights_count;