Trigger initialization of namespaces by GET request (containing user token)

[MatousJobanek]

Tenant service should not wait for the first POST call but should initialize namespaces when it receives first GET call containing user's token

[nurali-techie]

@MatousJobanek can you plz detailed out the motivation behind this changes (the why part) OR some issue encounter which need this changes.

[MatousJobanek]

@nurali-techie the motivation is to be ready for removing POST calls to tenant service when a user logs in - it's mentioned in the issue you have created if I'm not mistaken: #746
Anyway, the original motivation for removing the POST call is an error that tenant service sometimes gets for new users from auth service - it sometimes fails that the user still doesn't have OS token assigned so it is not possible to provision the namespaces

[nurali-techie]

@MatousJobanek thanks, as we are still discussing #746 I was not expecting any changes wrt to the issue at the same time I understand that #729 may impact #746 so I thought to check what's the original motivation for #729.