chore(sample): trust user CA in debug builds for MITM proxy testing

Adds a debug-only source set (sample/src/debug) with a network security config trusting system + user-added CAs, plus a manifest overlay wiring it in. Debug builds only; release artifacts are unaffected. Lets an intercepting proxy (e.g. Proxyman) decrypt the sample app's HTTPS for SDK network UAT.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: evan-masseau

sample/src/debug/AndroidManifest.xml

@@ -0,0 +1,10 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Debug-only manifest overlay. This source set is compiled into debug builds
+  ONLY, so release builds never see the networkSecurityConfig below. It opts
+  the sample into trusting user-added CA certs (see res/xml/network_security_config)
+  so an intercepting proxy (e.g. Proxyman) can MITM HTTPS during network testing.
+-->
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <application android:networkSecurityConfig="@xml/network_security_config" />
+</manifest>

sample/src/debug/res/xml/network_security_config.xml

@@ -0,0 +1,15 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Debug-only source set: present in debug builds exclusively (never packaged
+  into release artifacts). Trust the system CA store plus user-added CAs so an
+  intercepting proxy (e.g. Proxyman) can decrypt the sample's HTTPS traffic for
+  network testing.
+-->
+<network-security-config>
+    <base-config>
+        <trust-anchors>
+            <certificates src="system" />
+            <certificates src="user" />
+        </trust-anchors>
+    </base-config>
+</network-security-config>