Update metadata section in Augur to Auspice

[joverlee521]

Depends on release of nextstrain/augur#1384

Note the new option to use --metadata-columns to export metadata without needing to use as coloring in the "What metadata is exported" section of the "Augur to Auspice" docs.

docs.nextstrain.org/src/learn/augur-to-auspice.rst

Lines 423 to 439 in 2db33f1

	What metadata is exported
	-------------------------
	Augur has two main types of “metadata” which we'll refer to as
	“TSV-data” (provided with the ``--metadata`` argument) and “node-data”
	which are JSONs provided via ``--node-data`` (see :doc:`data formats </reference/data-formats>` for more).
	Typically, node-data information is automatically exported as a coloring whereas
	TSV-data must be explicitly exported by requesting it as a coloring in the
	auspice-config JSON. [#f3]_ Metadata is exported as a coloring if via the
	following process:
	- All key-value pairs specified in node-data JSONs, unless they match a
	hardcoded-list of exclusions and special-cases (next section). This
	has the effect that data provided in node-data JSONs will form a
	coloring and thus be exported in the dataset JSON.
	- Command-line provided colorings (not covered in this guide)
	- Colorings specified in the ``auspice_config.json`` (see below)

[joverlee521]

Noting that I chatted with @kimandrews in our 1:1 today about the metadata_columns feature. It was pretty confusing for me to remember the distinction of colorings, filters, and metadata_columns in the Auspice config JSON and I'm the one who added the new feature 😅

[jameshadfield]

I find reading the description / $comment in the schema to be helpful. One day we'll turn these schemas into docs!