[wip] attempt at limiting concurrent deploys

Since fetch_from_genbank can query NCBI up to 5 times for each of the serotypes, try to limit concurrent queries to under 3. Using 2 to be cautious.

Following the format shown at:
nextstrain/ncov#1045

ingest/workflow/snakemake_rules/fetch_sequences.smk

@@ -12,6 +12,7 @@ Produces final output as
     sequences_ndjson = "data/sequences_{serotype}.ndjson"
 
 """
+workflow.global_resources.setdefault("concurrent_deploys", 2)
 
 def download_serotype(wildcards):
     serotype = {
@@ -24,6 +25,8 @@ def download_serotype(wildcards):
     return serotype[wildcards.serotype]
 
 rule fetch_from_genbank:
+    resources:
+        concurrent_deploys=1,
     output:
         genbank_ndjson="data/genbank_{serotype}.ndjson",
     params: