Description of proposed changes

Copies the new Nextclade_pango column from nextclade.tsv to metadata.tsv. This column contains Pango lineages assigned using Nextclade.

Related issue(s)

Symmetrical PR in ingest: nextstrain/ncov-ingest#291

Testing

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Release checklist

If this pull request introduces backward incompatible changes, complete the following steps for a new release of the workflow:

• Determine the version number for the new release by incrementing the most recent release (e.g., "v2" from "v1").
• Update docs/src/reference/change_log.md in this pull request to document these changes and the new version number.
• After merging, create a new GitHub release with the new version number as the tag and release title.

If this pull request introduces new features, complete the following steps:

• Update docs/src/reference/change_log.md in this pull request to document these changes by the date they were added.