About: name the webmail node and the mail server node

Settings > About shows which webmail node answered (NODE_NAME, else the
container hostname) and which inbuxa node it talks to: the address the
server's name resolves to from the webmail, named by its PTR record. The
server only tells administrators its node name, so the webmail works it
out itself. Fetched from /api/about/nodes on every visit, cached for a
minute server-side, for troubleshooting a cluster.

Fork-only: upstream ihasmail runs one webmail against one server.
4 new strings, translated in all 9 catalogues.

server/src/config.ts

@@ -296,6 +296,12 @@ export const config = {
    * such a tree, so the default is INBUXA's fork.
    */
   sourceUrl: env("SOURCE_URL", "https://git.coffeylabs.org/inbuxa/ihasmail-inbuxa"),
+  /**
+   * ihasmail-inbuxa: this webmail's own name, shown in Settings > About next
+   * to the mail node it talks to. Set per host by the deploy; empty means the
+   * container's hostname. See nodes.ts.
+   */
+  nodeName: env("NODE_NAME", ""),
   host: env("HOST", "0.0.0.0"),
   port: int("PORT", 8080),
   /**