feat(deps): make https-proxy-agent optional (#2388)

Bump https-proxy-agent to v7 and a dev dependency. This makes
configuring bundlers easier to configure and removes a direct
dependency of `https-proxy-agent`.

BREAKING CHANGE: Configuring a proxy is done by specifying the
`agent` parameter on the ConnectionOptions config. This can use be
created by libraries such as `https-proxy-agent` or any that
implements `http.Agent`.

UNIQUE_SETUPS.md

@@ -62,12 +62,7 @@ To use `xrpl.js` with React, you need to install shims for core NodeJS modules.
             Buffer: ["buffer", "Buffer"],
           }),
         ]);
-
-        // This is deprecated in webpack 5 but alias false does not seem to work
-        config.module.rules.push({
-          test: /node_modules[\\\/]https-proxy-agent[\\\/]/,
-          use: "null-loader",
-        });
+        
         return config;
       };
       ```