Add helper methods to HTTPRequest to match original API

These methods are called by http_request_cb() and are present in the
original http_libevent::HTTPRequest.

src/httpserver.h

@@ -322,6 +322,16 @@ public:
     {
         WriteReply(status, std::as_bytes(std::span{reply_body_view}));
     }
+
+    // These methods reimplement the API from http_libevent::HTTPRequest
+    // for downstream JSONRPC and REST modules.
+    std::string GetURI() const { return m_target; }
+    CService GetPeer() const;
+    HTTPRequestMethod GetRequestMethod() const { return m_method; }
+    std::optional<std::string> GetQueryParameter(std::string_view key) const;
+    std::pair<bool, std::string> GetHeader(std::string_view hdr) const;
+    std::string ReadBody() const { return m_body; }
+    void WriteHeader(std::string&& hdr, std::string&& value);
 };
 
 class HTTPServer
@@ -520,6 +530,8 @@ private:
     void DisconnectClients();
 };
 
+std::optional<std::string> GetQueryParameterFromUri(std::string_view uri, std::string_view key);
+
 class HTTPRemoteClient
 {
 public: