api: BackendTrafficPolicy DNSLookupFamily

[guydc]

What type of PR is this?

What this PR does / why we need it:

• Makes it possible to define DNS lookup family for xRoute and non-xRoute BackendRefs.
• This is particularly useful when using the Backend resource, see Breaking change: Backend cluster DNS lookup is V4_PREFERRED #5247
• These settings will override any default configuration that Envoy Gateway autogenerates based on Service IpFamilies.

Which issue(s) this PR fixes:

Fixes #

Release Notes: In the implementation PR

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 65.03%. Comparing base (338b3c2) to head (0c53c02).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5249      +/-   ##
==========================================
+ Coverage   64.96%   65.03%   +0.06%     
==========================================
  Files         214      214              
  Lines       33532    33532              
==========================================
+ Hits        21785    21806      +21     
+ Misses      10407    10389      -18     
+ Partials     1340     1337       -3     

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[arkodg]

thanks @guydc, this looks good !
reg naming, does any other implementation have a similar setting

[guydc]

Some examples:

nginx:

• https://nginx.org/en/docs/http/ngx_http_upstream_module.html#resolver
• both IP families supported by default, and can be disabled with [ipv4=on|off] [ipv6=on|off] directives

istio:

• https://github.com/istio/istio/blob/cf37b2f305d5c8a51092a849bbb7ddb7017f52d7/operator/pkg/apis/values_types.pb.go#L1266
• IpFamilies (value: IPv4, IPv6) determine which IPFamilies are considered and in which order
• IpFamilyPolicy(values: PreferDualStack, RequireDualStack, and SingleStack.) Determines if IPFamilies defines an ordered list of preferences (e.g. Prefer IPv4 and Fallback to IPv6), a full dual stack solution (both IPv4 and IPv6) or just a single family.

contour:

• https://projectcontour.io/docs/1.30/config/api/#projectcontour.io/v1alpha1.ClusterDNSFamilyType
• 1-to-1 with envoy config pretty much.

F5:

• https://my.f5.com/manage/s/article/K12140128
• Use IPv6 and Use IPv4 flags

So, there's a variety of styles.

[arkodg]

thoughts on just IPv4 ? its less to type, but will it confuse the user who is aware of the envoyproxy api enums?

[arkodg]

LGTM thanks !