Server features should be []any, not []string

[dfawley]

grpc-go/internal/xds/bootstrap/bootstrap.go

Line 272 in 317271b

ServerFeatures []string `json:"server_features,omitempty"`

Per A30:

      // A list of features supported by the server.  New values will
      // be added over time.  For forward compatibility reasons, the
      // client will ignore any entry in the list that it does not
      // understand, ***regardless of type***.

(*'s added for emphasis)

We need to not fail to parse if other types are encountered here.

[dfawley]

It turns out Go's json umarshalling will result in an empty string instead of failing, so this may not be urgent.

https://go.dev/play/p/T-Qa9ygkcsC

Also, CC @ejona86 who says Java is (also?) decoding it as an array of strings, and @markdroth as FYI.

[dfawley]

I'm going to close this since we can just add support for non-string types (however that might work eventually) when we need them. We won't fail to parse newer configs that specify them with today's code.