Make configureHTTP2AsyncSecureUpgrade public (#480)

Minor PR to make `configureHTTP2AsyncSecureUpgrade ` helper function
public

Co-authored-by: George Barnett <[email protected]>

Author: adam-fowler

Sources/NIOHTTP2/HTTP2PipelineHelpers.swift

@@ -633,7 +633,7 @@ extension Channel {
     /// - Returns: An `EventLoopFuture` of an `EventLoopFuture` containing the `NIOProtocolNegotiationResult` that completes when the channel
     ///     is ready to negotiate.
     @inlinable
-    internal func configureHTTP2AsyncSecureUpgrade<HTTP1Output: Sendable, HTTP2Output: Sendable>(
+    public func configureHTTP2AsyncSecureUpgrade<HTTP1Output: Sendable, HTTP2Output: Sendable>(
         http1ConnectionInitializer: @escaping NIOChannelInitializerWithOutput<HTTP1Output>,
         http2ConnectionInitializer: @escaping NIOChannelInitializerWithOutput<HTTP2Output>