[Feature] Support GRPC "multi" mode introduced in Xray-core

[weaponmasterjax]

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• 我已经在 Issue Tracker 中找过我要提出的请求 I have searched on the issue tracker for a related feature request.
• 我已经仔细看过 Documentation 并无法找到这个功能 I have read the documentation and was unable to solve the issue.

Description

Xray-core has introduced GRPC multi mode which significantly increases connection speed with/without cdn. We'd better to add that feature as well and keep up with the original client's behaviours.

Possible Solution

No response