xdsclient/xdsresource: add AutoHostRewrite and Endpoint Hostname support

[Pranjali-2501]

This PR implements the validation logic and extracting per endpoint Hostname attributes from xDS resources for gRFC A81

Key Changes:

1. RDS Resource Validation :

   • The boolean value of RouteAction.auto_host_rewrite is extracted from the RDS resource and stored in route struct
   • This field is only set to true in the parsed route struct if the trusted_xds_server option is present in the ServerConfig and the global environment variable for authority overriding is enabled.

2. EDS Resource Validation:

   • The Endpoint.hostname field is extracted from the EDS resource and will be stored as a hostname string in parsed endpoint struct. It will be changed to be an per-endpoint resolver attribute in a follow-up PR.

RELEASE NOTES: None

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.19%. Comparing base (a764d3f) to head (d8f997f).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8728      +/-   ##
==========================================
- Coverage   83.21%   83.19%   -0.02%     
==========================================
  Files         419      419              
  Lines       32443    32454      +11     
==========================================
+ Hits        26997    27001       +4     
- Misses       4056     4064       +8     
+ Partials     1390     1389       -1     

Files with missing lines	Coverage Δ
internal/envconfig/envconfig.go	100.00% <ø> (ø)
internal/xds/xdsclient/xdsresource/filter_chain.go	93.92% <100.00%> (+0.55%)	⬆️
...ds/xdsclient/xdsresource/listener_resource_type.go	96.15% <100.00%> (ø)
...dsclient/xdsresource/route_config_resource_type.go	93.33% <100.00%> (ø)
...nternal/xds/xdsclient/xdsresource/unmarshal_eds.go	94.32% <100.00%> (+0.04%)	⬆️
...nternal/xds/xdsclient/xdsresource/unmarshal_lds.go	88.46% <100.00%> (ø)
...nternal/xds/xdsclient/xdsresource/unmarshal_rds.go	87.74% <100.00%> (+0.14%)	⬆️

... and 25 files with indirect coverage changes

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[easwars]

The PR description says:

• This string value is included as a per-endpoint resolver attribute (hostname) in the parsed resource struct.

But the PR only stores it as a string, and not as a resolver attribute. The per-endpoint resolver attribute is defined here:

grpc-go/resolver/resolver.go

Line 191 in 69769dc

Attributes *attributes.Attributes

This means that the parsed Endpoint struct defined here:

grpc-go/internal/xds/xdsclient/xdsresource/type_eds.go

Line 51 in 69769dc

type Endpoint struct {

needs to be changed to contain a resolver.Endpoint instead of a slice of address strings, and the newly added HostName field and some of the other existing things like Weight and HashKey also need to move into the endpoint attributes. This is probably big enough to be made as a separate PR though. Let's discuss this offline.

But for now, maybe the PR description need to be modified though to state that we are only storing it as a string for now and that in a follow-up PR we will change it to be an endpoint attribute.

[easwars]

LGTM modulo minor nits

[easwars]

Nit: Can we make this field be of type xdsclient.ServerFeature instead?

[Pranjali-2501]

Done.

[easwars]

Nit: The assignment and the conditional can be on the same line.

[Pranjali-2501]

Done.