Improve EDNS handling

[DL6ER]

What does this implement/fix?

This PR merges a few EDNS related changes:

• Add downstream EDE info for synthesized replies
  This commit enriches downstream DNS replies with blocking information. This can be controlled (and also disabled) via the new setting dns.blocking.edns.
  Example:
  

• Add EDE 15 from upstream => Blocked detection
  Pi-hole already detects NXRA (NXDOMAIN without RA bit from Quad9 or unbound with option rpz-signal-nxdomain-ra), NULL address (0.0.0.0 / ::) and a set of known IP addresses (Cisco Umbrella) to determine a query was blocked upstream. This PR adds a new detection that is a query has EDE 15 = Blocked set by the upstream resolver. This can be seen, e.g. in routeDNS which is used by the user requesting this feature.

• Unify query and cache status enums
  This is mostly a code maintenance commit without any externally visible changes. It removes the enum domain_client_status in favor of the more generic enum query_status.

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Related issue or feature (if applicable): N/A

Pull request in docs with documentation (if applicable): pi-hole/docs#1094

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[yubiuser]

Do we need amendments to the docs for the new database query status QUERY_EXTERNAL_BLOCKED_EDE15?

[DL6ER]

See pi-hole/docs#1094

[rdwebdesign]

Do we need to change the web interface to show this new value?

[DL6ER]

@rdwebdesign No, in v6, we query FTL for the defined types and, hence, no web code changes are necessary if new types are added.

[rdwebdesign]

no web code changes are necessary if new types are added.

Cool!