Add support for DNSTAP
    
    Not enabled by default yet. Enables dumping of dns traffic.
    Fix DNSTAP issues in build and unit tests.
    
    Fool rpmlint to accept dnstap relative path. Rpmlint emited error
    hardcoded-library-path on dnstap path. It is not system-wide library,
    workaround by using variable.
    
    Add dnstap-read utility to utils. When dnstap is enabled,
    dnstap-read will be part of utils. Disadvantage is all utilities would have
    dependency on protobuf library, including host and dig.
    
    Resolves: #1564776