certs: add 'DigiCert Global Root G3'...

... for quad9.net which can be used for DoH:

$CertificateAvailable "DigiCert Global Root G3";
/ip/dns/set use-doh-server=https://9.9.9.9/dns-query verify-doh-cert=yes;

certs/DigiCert-Global-Root-G3.pem

@@ -0,0 +1,22 @@
+# Issuer: CN=DigiCert Global Root G3 O=DigiCert Inc OU=www.digicert.com
+# Subject: CN=DigiCert Global Root G3 O=DigiCert Inc OU=www.digicert.com
+# Label: "DigiCert Global Root G3"
+# Serial: 7089244469030293291760083333884364146
+# MD5 Fingerprint: f5:5d:a4:50:a5:fb:28:7e:1e:0f:0d:cc:96:57:56:ca
+# SHA1 Fingerprint: 7e:04:de:89:6a:3e:66:6d:00:e6:87:d3:3f:fa:d9:3b:e8:3d:34:9e
+# SHA256 Fingerprint: 31:ad:66:48:f8:10:41:38:c7:38:f3:9e:a4:32:01:33:39:3e:3a:18:cc:02:29:6e:f9:7c:2a:c9:ef:67:31:d0
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----