[Workspace] Support workspace initial page

[yubonluo]

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

Support workspace initial page:

• If login user has no workspace, it would show the initial page
• If login user has more than one workspaces, it would not show the initial page
• Dashboard admin can click the create workspace button
• Create workspace button do not been shown for non admin user

Describe the solution you'd like
mockup:

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

Additional context
#4944