ingest: Merge Nextclade metadata with augur merge

This construction reads a bit clearer and cleaner.  It's also a good
example of how to use `augur merge`.

The limitation on non-seekable streams means the rule now uses
additional transient disk space, but it typically shouldn't be an issue.
The way Augur's slow start up time impacts `augur merge` also
contributes to a longer rule execution time, but it should be negligible
in the context of the larger workflow and presumably we'll fix the slow
start up eventually.¹

The output is semantically identical but has some syntactic changes re:
quoting.  It's worth noting that the pre-existing TSV format was _not_
IANA TSV, despite it (still) being treated as such in a few places, but
was (and remains) a CSV-like TSV with some quoted fields (and some
mangled quotes², e.g. the "institution" column for accession KJ556895).
We really need to sort out our TSV formats³, but that's for a larger
project.

¹ <nextstrain/augur#1628>
² <nextstrain/augur#1565>
³ <nextstrain/augur#1566>

ingest/rules/nextclade.smk

@@ -62,6 +62,7 @@ rule join_metadata_and_nextclade:
         metadata="data/subset_metadata.tsv",
     output:
         metadata="results/metadata.tsv",
+        nextclade_metadata=temp("results/nextclade_metadata.csv"),
     params:
         metadata_id_field=config["curate"]["output_id_field"],
         nextclade_id_field=config["nextclade"]["id_field"],
@@ -75,13 +76,15 @@ rule join_metadata_and_nextclade:
             --field-map {params.nextclade_field_map:q} \
             --output-metadata - \
         | tsv-select --header --fields {params.nextclade_fields:q} \
-        | tsv-join -H \
-            --filter-file - \
-            --key-fields {params.nextclade_id_field} \
-            --data-fields {params.metadata_id_field} \
-            --append-fields '*' \
-            --write-all ? \
-            {input.metadata} \
-        | tsv-select -H --exclude {params.nextclade_id_field} \
-            > {output.metadata}
-        """    
+        > {output.nextclade_metadata:q}
+
+        augur merge \
+            --metadata \
+                metadata={input.metadata:q} \
+                nextclade={output.nextclade_metadata:q} \
+            --metadata-id-columns \
+                metadata={params.metadata_id_field:q} \
+                nextclade={params.nextclade_id_field:q} \
+            --output-metadata {output.metadata:q} \
+            --no-source-columns
+        """