Title: XFCC in APPEND_FORWARD or SANITIZE_SET only uses the first URI present

Description:

Presently only the first SAN URI is preserved in XFCC headers. For users that have multiple SAN URIs no information is propagated in the By= and URI= portion of the XFCC header.

While some users use spiffe:// and spiffe:// only there are others that need other URI information.

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Envoy XFCC docs