Feature Request: Add hint to support routing queries to vttablet by tablet alias

[earayu]

Issue Content:

Currently, WeSQL-Scale supports routing queries to vttablets using keyspace, shard, and tablet types as routing keys. However, it would be beneficial to enhance the query routing mechanism by adding support for routing queries to vttablets using tablet aliases.

We propose the following feature request:

1. Support Query Routing by Tablet Alias: Modify WeSQL-Scale to allow routing queries to a specific vttablet using its tablet alias as an additional routing key. This would provide more flexibility in directing queries to specific tablets within a shard.

With this feature, users will have the ability to precisely control query routing to vttablets, which can prove useful in scenarios where specific tablets need to handle certain types of queries or for targeted troubleshooting.

We appreciate your valuable feedback and suggestions on this feature request.