Move tikv-importer to lightning chart

[shonge]

Feature Request

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

Importer in tidb-cluster chart and it work need lightning together, so maybe we should move it to the lightning chart.

Describe the feature you'd like:

Install or remove lightning/importer in one step.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy:

[Yisaer]

As we are moving attention from helm chart to CRD Object, the new feature request or refactor is preferred to be done in CRD Object. What's your opinion? @aylei

[DanielZhangQD]

I think no need to create CRD and controller for lightning and importer since they are just one-time deal tools.
Lightning does not have to work together with the importer, it supports two backends - tidb/mysql (https://pingcap.com/docs/stable/reference/tools/tidb-lightning/tidb-backend/) and importer.
But from v1.1, tidb cluster is migrated to CRD, and now we cannot install importer with helm, I think we can add tikv-importer to lightning chart and with enable to control whether to deploy importer when deploying lightning.

DBaaS may need this when switching to operator v1.1.
Please also note that tikv-importer functions will be integrated into lightning/tikv in the tool's roadmap in v4.0, however, we are not sure when will that be completed.

[DanielZhangQD]

@shonge Suggest adding a new chart for tikv-importer instead of updating the chart of tidb-lightning since they do not need to be deployed together.