Move http2 out of experimental

Http2 support in bmcweb has been relatively stable for a while.  The
http2 implementation passes all known Redfish tests (some of which
require ported to httpx to support http2), the UI loads, and so far as
the project is concerned, is a complete improvement over the existing
http1 stack.

This commit removes the experimental classification from http2, and
declares it ready for production use, while enabling it by default.
note, that enabling this by default only makes the server advertise that
http2 is available.  Http2 must still be supported by the client to
enable ALPN negotiation, so existing http1 clients that only support
http1 will continue to function as they did before.

Tested: Enabled http option and saw http2 advertised, http2 now takes
effect.

Change-Id: I92843a3afc532f0b2a64904bb872e5d84a1a54fe
Signed-off-by: Ed Tanous <etanous@nvidia.com>
diff --git a/src/ssl_key_handler.cpp b/src/ssl_key_handler.cpp
index 128d1f2..f1442b9 100644
--- a/src/ssl_key_handler.cpp
+++ b/src/ssl_key_handler.cpp
@@ -578,7 +578,7 @@
 
     SSL_CTX_set_options(sslCtx.native_handle(), SSL_OP_NO_RENEGOTIATION);
 
-    if constexpr (BMCWEB_EXPERIMENTAL_HTTP2)
+    if constexpr (BMCWEB_HTTP2)
     {
         SSL_CTX_set_next_protos_advertised_cb(sslCtx.native_handle(),
                                               nextProtoCallback, nullptr);