Add ALPN support to the pools service client

This patch adds ALPN protocol selection support to the pools service
client allowing you to limit the ALPN protocols negotiated when connecting
to member servers.

A follow on patch should include test coverage for this.

Change-Id: Id0b93446dbfdde479fd573eed3e9a5c1e9400609
diff --git a/releasenotes/notes/pools-service-client-alpn-support-7de3bcd3c901ff1a.yaml b/releasenotes/notes/pools-service-client-alpn-support-7de3bcd3c901ff1a.yaml
new file mode 100644
index 0000000..e7554e2
--- /dev/null
+++ b/releasenotes/notes/pools-service-client-alpn-support-7de3bcd3c901ff1a.yaml
@@ -0,0 +1,4 @@
+---
+features:
+  - |
+    Added support for ALPN selection in the pools service client.