[dnssd] support forwarding DNS queries to platform upstream (#8668)

This commit adds a set of APsI for forwarding a DNS query to the
upstream DNS server via platform API and a posix platform
implementation.

This feature is disabled by default, and this PR adds a `dns server
upstream {enable|disable}` command CLI for enabling and disabling this
feature.

Tests will be added after ot-br-posix adds related support.

script/make-pretty

@@ -108,6 +108,7 @@ OT_CLANG_TIDY_BUILD_OPTS=(
     '-DOT_DIAGNOSTIC=ON'
     '-DOT_DNS_CLIENT=ON'
     '-DOT_DNS_DSO=ON'
+    '-DOT_DNS_QUERY_UPSTREAM=ON'
     '-DOT_DNSSD_SERVER=ON'
     '-DOT_DUA=ON'
     '-DOT_MLR=ON'