[Feature] vela-apiserver supports mysql driver

[oeular]

In vela-apiser, there are two drivers (kubeapi and mongodb) to save the metadata, and now mysql driver is needed.

[oeular]

For some reasons, mysql driver is needed:

• the LIST operation for configmaps will get all configmaps in namespace which makes request pressure for k8s apiserver, and this is high latency, but mysql driver can low the latency by db index.
• the configmaps for metadata will increase highly with the increasing of applications and components, but mysql can scale up easily and in safety.
• with mysql driver, it's high-available and high-reliability naturally.

[oeular]

@tangoliu
we discuss this issue here.

[oeular]

In this issue, it will be much better to provide the API or vela-cli for migrating the metadata from kube-api to mysql, and it's optional for migrating from mongodb to mysql.

[chivalryq]

duplicate with #3666

[oeular]

OK. But migrating the metadata among the mongodb, kube-api and mysql could be an independent feature.

[wonderflow]

kubevela/velaux#841