phylogenetic: support standardized multiple input

[joverlee521]

We have converged on a generic pattern for defining multiple inputs in nextstrain/pathogen-repo-guide#91.

This will be added in addition to the custom config params currently used for the inrb builds

mpox/phylogenetic/build-configs/inrb/config.yaml

Lines 9 to 11 in f1bf4f8

	# INRB builds inject private data, which is itself created by calling `curate_private_data.py`
	private_sequences: "data/sequences-private.fasta"
	private_metadata: "data/metadata-private.tsv"

Noting that the current workflow merges the private data after the filter rule to bypass the filter query. The new pattern would merge before the filter rule.

[joverlee521]

Edited the issue contents to reflect reality in #339 where I'm added the standardized multiple input support in addition to the private sequences merge.