Enhance tiup client to list TiProxy instances as endpoints

[alastori]

Feature Request

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

Currently, when using the tiup client, it only displays a list of available endpoints that includes TiDB instances. This limitation can be frustrating for users who also want to connect to TiProxy instances, as they are not listed in the output.

Describe the feature you'd like:

I would like the tiup client to be enhanced to include TiProxy instances in the list of available endpoints alongside TiDB instances.

Why the feature is needed:

Including TiProxy instances in the endpoint listing will provide users with a more comprehensive view of all available endpoints. This is particularly useful in scenarios where users need to connect to both TiDB and TiProxy instances for load balancing or proxying purposes. It simplifies the connection process and enhances the overall user experience.

Describe alternatives you've considered:

Currently, users have to manually check for TiProxy instances or use separate commands to identify them, which can be cumbersome. Then they need to use another client, like the MySQL standard client, instead of tiup client to connect to TiProxy instances. This requires the installation and use of another client. Integrating TiProxy endpoints into the existing tiup client command would be more user-friendly.

Teachability, Documentation, Adoption, Migration Strategy:

• Documentation should be updated to reflect this change, explaining how users can now see both types of instances when they run the tiup client command.
• This change doesn't break existing behavior of existing features.

Solution idea

• Update the scanEndpoint function in components/client/main.go to include both TiDB and TiProxy instances in the endpoint listing. Check for TiDB and TiProxy instances, perhaps by adding a new functions to identify them (e.g., isTiProxyInstance, to identify TiProxy instances based on their naming convention - instances that start with "tiproxy-").

[alastori]

/label category/usability

[ti-chi-bot[bot]]

@alastori: The label(s) category/usability cannot be applied. These labels are supported: help wanted, good first issue.

In response to [this](https://github.com/pingcap/tiup/issues/2473#issuecomment-2465264212): >/label category/usability Instructions for interacting with me using PR comments are available [here](https://prow.tidb.net/command-help). If you have questions or suggestions related to my behavior, please file an issue against the [ti-community-infra/tichi](https://github.com/ti-community-infra/tichi/issues/new?title=Prow%20issue:) repository.