Support to install lws at user specified namespace

[kerthcet]

What would you like to be added:

Hope to install lws at a configurable namespace rather than the hardcode lws-system.

Here's a code snippet we need to care about: https://github.com/kubernetes-sigs/lws/blob/main/pkg/cert/cert.go#L27

Why is this needed:

Completion requirements:

This enhancement requires the following artifacts:

• Design doc
• API change
• Docs update

The artifacts should be linked in subsequent comments.

[googs1025]

/assign
I understand that we need to provide a configurable namespace right?

[liurupeng]

+1 to the proposal

[googs1025]

#170

Is it consistent with this issue?

[googs1025]

/unassign

[kerthcet]

Yes, this should be part of the CC, would you like to take it over @googs1025