fix: infinite proxy loop (#4676)

I think the problem is that when a proxy is not in use proxy-agent
returns the global agent...which is itself since we set it globally,
causing the loop.

VS Code already covers proxies meaning we only need to do it in our own
requests so to fix this pass in the agent in the version fetch request
instead of overidding globally.

Also avoid proxy-from-env and pass in the proxy URI instead as both
http_proxy and https_proxy can be used for either http or https requests
but it does not allow that.

src/node/update.ts

@@ -1,9 +1,10 @@
 import { field, logger } from "@coder/logger"
 import * as http from "http"
 import * as https from "https"
+import ProxyAgent from "proxy-agent"
 import * as semver from "semver"
 import * as url from "url"
-import { version } from "./constants"
+import { httpProxyUri, version } from "./constants"
 import { SettingsProvider, UpdateSettings } from "./settings"
 
 export interface Update {
@@ -102,8 +103,10 @@ export class UpdateProvider {
     return new Promise((resolve, reject) => {
       const request = (uri: string): void => {
         logger.debug("Making request", field("uri", uri))
-        const httpx = uri.startsWith("https") ? https : http
-        const client = httpx.get(uri, { headers: { "User-Agent": "code-server" } }, (response) => {
+        const isHttps = uri.startsWith("https")
+        const agent = httpProxyUri ? new ProxyAgent(httpProxyUri) : undefined
+        const httpx = isHttps ? https : http
+        const client = httpx.get(uri, { headers: { "User-Agent": "code-server" }, agent }, (response) => {
           if (!response.statusCode || response.statusCode < 200 || response.statusCode >= 400) {
             response.destroy()
             return reject(new Error(`${uri}: ${response.statusCode || "500"}`))