Support rbac control for the data access

[Yisaer]

Feature Request

Is your feature request related to a problem? Please describe:

Currently, the user who have the pd address will have the ability to do every action in pd and tikv (read/write/delete). However, in real world users might need to have the different rights to access the data. (like mysql rbac control)

Describe the feature you'd like:

Adding rbac control for the TiKV and PD so that each request for access data to TiKV and PD will be checked by authorization and authentication.

The whole task would be split into following steps:

• design authorization and authentication for PD to control the whole rbac process.
• support authorization and authentication in PD for the PD API by rbac control
• support rbac ability for pdclient in TiKV
• support authorization and authentication in TiKV (metadata would be saved in PD)
• support rbac ability for tikv-client.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

The detailed design document would be released recently by @Yisaer

[rleungx]

This issue is for the TiKV CommunityBridge project. Mentee candidates who want to participate in CommunityBridge with the TiKV project are expected to join Slack Channel to have self-introductions before applying.