cmake: Add OpenSSL dependency check in configuration

This enables projects having to
only find libcoap in their cmake
and not openssl too.

cmake/Config.cmake.in

@@ -2,3 +2,20 @@
 
 include("${CMAKE_CURRENT_LIST_DIR}/@PROJECT_NAME@Targets.cmake")
 check_required_components("@PROJECT_NAME@")
+
+include(CMakeFindDependencyMacro)
+if (@WITH_GNUTLS@)
+    find_dependency(GnuTLS)
+endif()
+if (@WITH_OPENSSL@)
+    find_dependency(OpenSSL)
+endif()
+if (@WITH_MBEDTLS@)
+    find_dependency(MbedTLS)
+endif()
+if (@WITH_WOLFSSL@)
+    find_dependency(WolfSSL)
+endif()
+if (@WITH_TINYDTLS@ AND NOT @USE_VENDORED_TINYDTLS@)
+    find_dependency(TinyDTLS)
+endif()