Support built-in VIP Management

[djshow832]

Feature Request

Describe your feature request related problem

In a self-hosted TiDB cluster with TiProxy, TiProxy is typically the endpoint for clients. To achieve high availability, users may deploy multiple TiProxy instances and only one serves requests so that the client can configure only one database address. When the active TiProxy is down, the cluster should elect another TiProxy automatically and the client doesn't need to update the database address.

Describe the feature you'd like

So we need a VIP solution. The VIP is always bound to an available TiProxy node. When the active node is down, VIP is switched to another node.

Describe alternatives you've considered

None

Teachability, Documentation, Adoption, Migration Strategy

None

Tasks

• RFC: Support built-in VIP Management #584
• Create a general elector #587
• Bind the VIP to the active node #589
• Integrate the VIP manager into the server #591
• Add a metric to check the active node #593