[UI] Default namespace should be username

[rtpro]

When deploying an app or a helm chart, set namespace as the currently logged-in user name.

• [x] Applications screen > Deploy App Modal
• [x] Catalog > Deploy app modal
• [x] Helm > Charts > Deploy chart modal

Namespaces can be only AlphaNumeric, thus when using the username as a namespace it should:

• [x] Replace @ with -- (2 dashes)
• [x] Replace any non-AlphaNumeric character with -. (dash)