reverse_tunnels: integration tests (#43840)

**Commit Message:** This PR adds basic integration tests for the reverse
tunnels functionality.

**Additional Description:**

This PR adds integration tests for the reverse tunnel functionality,
including:

1. **EndToEndReverseTunnelTest** - Tests basic reverse tunnel setup with
a single node establishing a connection to a cloud listener, followed by
sending HTTP requests through the egress listener that route through the
reverse tunnel to a backend service. Validates the complete
request/response flow and verifies tunnel statistics.

2. **EndToEndReverseTunnelTestWithMutualTLS** - Similar to the basic
end-to-end test but with mutual TLS (mTLS) between the initiator and
responder.

3. **ReverseTunnelResiliencyTest** - Tests reverse tunnel resilience in
a multi-node, multi-cloud scenario. Sets up 2 edge nodes (node-1,
node-2) with connections to 2 cloud instances (cloud_1, cloud_2) using
LDS. Simulates node-1 failure by removing its initiator listeners via
LDS, verifies that node-2 continues to function while node-1 requests
fail, then re-adds node-1's listeners and confirms that tunnels are
re-established and both nodes become operational again.

4. **MultiWorkerEndToEndReverseTunnelTest** - Test that runs the
complete e2e test but with multiple workers.

**Risk Level:** Low - Tests only

**Testing:** New integration tests added

**Docs Changes:** N/A

**Release Notes:** N/A

**Platform Specific Features:** N/A

---------

Signed-off-by: Basundhara Chakrabarty <basundhara.c@nutanix.com>
Signed-off-by: Basundhara Chakrabarty <basundhara17061996@gmail.com>

Author: basundhara-c

test/extensions/clusters/reverse_connection/BUILD

@@ -3,6 +3,10 @@ load(
     "envoy_cc_test",
     "envoy_package",
 )
+load(
+    "//test/extensions:extensions_build_system.bzl",
+    "envoy_extension_cc_test",
+)
 
 licenses(["notice"])  # Apache 2
 
@@ -36,3 +40,44 @@ envoy_cc_test(
         "@envoy_api//envoy/extensions/clusters/reverse_connection/v3:pkg_cc_proto",
     ],
 )
+
+envoy_extension_cc_test(
+    name = "reverse_connection_cluster_integration_test",
+    size = "large",
+    srcs = ["reverse_connection_cluster_integration_test.cc"],
+    extension_names = [
+        "envoy.clusters.reverse_connection",
+        "envoy.filters.network.reverse_tunnel",
+        "envoy.filters.http.lua",
+        "envoy.bootstrap.reverse_tunnel.upstream_socket_interface",
+        "envoy.bootstrap.reverse_tunnel.downstream_socket_interface",
+        "envoy.resolvers.reverse_connection",
+        "envoy.transport_sockets.tls",
+    ],
+    rbe_pool = "6gig",
+    deps = [
+        "//source/common/protobuf:utility_lib",
+        "//source/extensions/bootstrap/reverse_tunnel/downstream_socket_interface:reverse_connection_resolver_lib",
+        "//source/extensions/bootstrap/reverse_tunnel/downstream_socket_interface:reverse_tunnel_initiator_lib",
+        "//source/extensions/bootstrap/reverse_tunnel/upstream_socket_interface:reverse_tunnel_acceptor_lib",
+        "//source/extensions/clusters/reverse_connection:reverse_connection_lib",
+        "//source/extensions/filters/http/lua:config",
+        "//source/extensions/filters/http/router:config",
+        "//source/extensions/filters/network/http_connection_manager:config",
+        "//source/extensions/filters/network/reverse_tunnel:config",
+        "//source/extensions/transport_sockets/tls:config",
+        "//test/integration:http_integration_lib",
+        "//test/integration:integration_lib",
+        "//test/test_common:environment_lib",
+        "//test/test_common:logging_lib",
+        "//test/test_common:utility_lib",
+        "@envoy_api//envoy/config/bootstrap/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/clusters/reverse_connection/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/filters/http/lua/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/filters/network/reverse_tunnel/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/transport_sockets/internal_upstream/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/transport_sockets/tls/v3:pkg_cc_proto",
+        "@envoy_api//envoy/extensions/upstreams/http/v3:pkg_cc_proto",
+        "@envoy_api//envoy/service/discovery/v3:pkg_cc_proto",
+    ],
+)