schemas: Update display_defaults.branch_label for Auspice v2 config a…

…nd dataset

Reconciles the two schemas with some minor improvements + a bug fix.
While the enum values in one schema were valid, they're not the _only_
valid values.

This display_default refers to the keys of branch_attr.labels objects on
nodes, so I reused the former's pattern of allowed characters.  I think
that pattern may be too restrictive and not accurately describe what
Auspice will handle, but that's a broader issue with other parts of the
schema too and something to investigate for another day.

Hint that there's a special-cased value ("none") by mentioning it
explicitly in the pattern.

augur/data/schema-auspice-config-v2.json

@@ -176,8 +176,10 @@
                     "enum": ["rect", "radial", "unrooted", "clock"]
                 },
                 "branch_label": {
+                    "description": "What branch label should be displayed by default, or 'none' to hide labels by default.",
+                    "$comment": "Should be a key present in the per-node branch_attrs.labels object of the exported JSON; pattern is from the schema for that object",
                     "type": "string",
-                    "enum": ["clade", "aa", "none"]
+                    "pattern": "^(none|[a-zA-Z0-9]+)$"
                 },
                 "transmission_lines": {
                     "type": "boolean"

augur/data/schema-export-v2.json

@@ -258,8 +258,10 @@
                             "type": "boolean"
                         },
                         "branch_label": {
-                            "description": "What branch label should be displayed by default.",
-                            "type": "string"
+                            "description": "What branch label should be displayed by default, or 'none' to hide labels by default.",
+                            "$comment": "Should be a key present in the per-node branch_attrs.labels object of the exported JSON; pattern is from the schema for that object",
+                            "type": "string",
+                            "pattern": "^(none|[a-zA-Z0-9]+)$"
                         },
                         "transmission_lines": {
                             "description": "Should transmission lines (if available) be displaye by default",