pw_tls_client: Add entropy facade

Add entropy facade in pw_tls_client for users to provide an entropy
source.

Change-Id: I0576971ea0f69f8967658db3270bcbdd3dd89668
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/50161
Commit-Queue: Yecheng Zhao <zyecheng@google.com>
Reviewed-by: Ali Zhang <alizhang@google.com>
diff --git a/pw_tls_client/BUILD b/pw_tls_client/BUILD
index 93bf559..01fa582 100644
--- a/pw_tls_client/BUILD
+++ b/pw_tls_client/BUILD
@@ -46,3 +46,15 @@
 
 # TODO(zyecheng): Add a "backend_multiplexer" target once BoringSSL/MbedTLS is
 # ready.
+
+pw_cc_facade(
+    name = "pw_tls_client_entropy_facade",
+    hdrs = [
+        "public/pw_tls_client/entropy.h",
+    ],
+    includes = ["public"],
+    deps = [
+        "//pw_bytes",
+        "//pw_status",
+    ]
+)