Add optional tags field for route rules

[Pushkinmazila2]

This PR adds optional tag support for individual rules.

Currently tags are supported for rule-sets, but not for standalone rules.
This change extends the same concept to regular rules to improve configuration structure and readability.

Example:

{
  "tag": "streaming",
  "domain_suffix": [
    "youtube.com",
    "netflix.com"
  ],
  "outbound": "proxy"
}

Motivation

Large configurations often contain many inline rules without an easy way to identify or group them.

Adding tags to rules helps:

• improve config maintainability
• simplify navigation in large configs
• prepare groundwork for possible future conditional/tag-based processing

Compatibility

This change is fully backward compatible:

• tag is optional
• existing configurations continue to work unchanged

[Pushkinmazila2]

The tag field (with a small letter), and the Tag() is method.:

[Pushkinmazila2]

I suggest integrating tag before the architecture runs away again )
@nekohasekai