[FR] Support for grouping Clash subscription nodes.

[sigeshuo]

Feature description

Some subscription addresses provide well-organized groups of subscription nodes. For example, in China, only proxies from certain countries support access to ChatGPT. If we only select a single node and that node encounters an issue, the proxy connection will not work properly. However, if there is a group of proxies specifically for ChatGPT, I only need to select that group. This group contains multiple node information, which prevents the situation where the entire service becomes unavailable due to the failure of a few nodes.

[titancomputer]

PR welcomed