private observations

[elecaude]

In some cases it's necessary to have "private" observations which would need to be authenticated in order to access them.
These kind of observations are sensitive and should not be seen by everyone.
These observations should have an owner and read / write rights given to other users
This requires adding a user management in the FROST server

[sgrellet]

Need apparently shared with AIT Austrian Institute of Technology.
Filtering could easily make you slip to private obs -> to handle this could cause major perf issues