Add send-report-channel option

This commit adds support for the EDNS Report-Channel option,
which is returned in authoritative responses when EDNS is in use.

"send-report-channel" sets the Agent-Domain value that will be
included in EDNS Report-Channel options.  This is configurable at
the options/view level; the value is a DNS name. Setting the
Agent-Domain to the root zone (".") disables the option.

When this value has been set, incoming queries matchng the form
_er.<qtype>.<qname>.<extended-error-code>._er.<agent-domain>/TXT
will be logged to the dns-reporting-agent channel at INFO level.

(Note: error reporting queries will only be accepted if sent via
TCP or with a good server cookie.  If neither is present, named
returns BADCOOKIE to complete the DNS COOKIE handshake, or TC=1
to switch the client to TCP.)

util/check-categories.sh

@@ -16,6 +16,7 @@ list1=$(
     | grep -E "^[[:space:]]+[^[:space:]]+_LOGCATEGORY_[^[:space:]]+([[:space:]]+=[[:space:]]+[-0-9]+)?," \
     | grep -Ev "ISC_LOGCATEGORY_(MAX|INVALID)" \
     | sed -e 's/.*LOGCATEGORY_\([A-Z_]*\).*/\1/' -e 's/^RRL$/rate-limit/' \
+      -e 's/DRA/dns-reporting-agent/' \
     | tr 'A-Z' 'a-z' \
     | tr _ - \
     | sed 's/^tat$/trust-anchor-telemetry/' \