bind9/bin/tests/system/doth

DoH query values that can be passed on the command line for testing
with curl can be obtained by encoding binary DNS messages into
base64url, with trailing '='s removed.

For example:

$ perl bin/tests/system/fromhex.pl << EOF | base64url
    # Transaction ID
    0001
    # Standard query
    0000
    # Questions: 1, Additional: 0
    0001 0000 0000 0000
    # QNAME: example
    07 6578616d706c65 00
    # Type: SOA
    0006
    Class: IN
    0001
EOF

This produces the string "AAEAAAABAAAAAAAAB2V4YW1wbGUAAAbFrMonAAE=". With
the trailing '=' removed, this can then be passed to curl:

curl "https://<server>/dns-query?dns=AAEAAAABAAAAAAAAB2V4YW1wbGUAAAbFrMonAAE"