dns_filter: Add TCP listener support for DNS resolution

*Title*: *One line description*
dns_filter: Add TCP listener support for DNS resolution

*Description*:

Summary

The UDP DNS filter (envoy.filters.udp.dns_filter) currently only supports UDP. This proposal
adds TCP DNS listener support to handle clients that use TCP for DNS resolution (e.g., via
options use-vc in resolv.conf, or applications that explicitly configure TCP DNS).

Use Case

We're building a service mesh feature where Envoy acts as the authoritative DNS resolver for
service discovery within a task/pod. The DNS filter resolves service names from an inline DNS
table and forwards unknown queries to upstream resolvers.

While UDP covers ~99% of DNS traffic, some scenarios require TCP:

- Clients configured with options use-vc in /etc/resolv.conf
- Applications using DNS libraries with explicit TCP transport (Go's net.Resolver with TCP
dial, Java's Netty DnsNameResolverBuilder)
- Fallback when UDP responses are truncated (TC bit set)

Without TCP support, these clients fail to resolve — the DNS filter can't fall back gracefully
since it only binds a UDP listener.

Proposed Behavior

- Add a TCP listener filter equivalent to the existing UDP DNS filter
- Reuse the same DnsFilterConfig (server_config, client_config, access_log) for consistency
- Support the same inline DNS table and external upstream forwarding
- Handle DNS message framing over TCP (2-byte length prefix per RFC 1035 §4.2.2)

Related

- Existing UDP DNS filter: envoy.filters.udp.dns_filter
- PR for reference (if you want to link your existing PR):
https://github.com/envoyproxy/envoy/pull/45615 (https://github.com/envoyproxy/envoy/pull/45615)

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[optional *Relevant Links*:]
>Any extra documentation required to understand the issue.

Start by reviewing the existing envoy.filters.udp.dns_filter and its DnsFilterConfig, then read RFC 1035 §4.2.2 and the referenced PR #45615 for context. Done means a TCP listener supports the same inline DNS table and upstream forwarding while correctly handling the 2-byte TCP DNS message length prefix.

Written by the indexing model from the issue text.