Allow user to add description of newly created namespace

[nirajCITZ]

As an api-owner, I would like to add description for newly created namespace
So that anyone can easily identify the purpose and content of the Gateway

[ikethecoder]

@nirajCITZ Is this for the Portal or the CLI? I don't think we are intending to enhance the create namespace in the portal - more likely removing it.

[rustyjux]

Addressed with the display name attribute added in Namespace to Gateway changes.