Update Slack channels to new CNCF Slack channels

[terrytangyuan]

cc @kubeflow/kubeflow-steering-committee

[andreyvelich]

I think we should keep two buttons, one for "CNCF Slack" and one for "Legacy Kubeflow Slack", at least until we finish the migration and archive all channels that people could want.

@thesuperzapper What is the reason to ask new folks to join the legacy Kubeflow Slack if we agreed to migrate to CNCF ? That will just complicate and slow-down our migration.

[terrytangyuan]

I think we should continue to link people to both until we finish the migration.

I don't think that's necessary. We never did that for Argo project. We only need to point to new folks to the new channels and in the meantime notifying existing Kubeflow Slack users to join the new channels.

[rimolive]

+1 to link only the new Slack channels.

[johnugeorge]

/lgtm

[johnugeorge]

/lgtm

[andreyvelich]

/approve

[google-oss-prow[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andreyvelich

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[content/en/docs/about/OWNERS](https://github.com/kubeflow/website/blob/master/content/en/docs/about/OWNERS)~~ [andreyvelich] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[jbottum]

/lgtm