Support R server profiles

[ymarcon]

When creating a new DataSHIELD R session on the R server side, it should be possible to specify which flavor of R server setup is to be used at login time.

For instance for a given DS node, there could be R servers with different R versions and/or different R/DataSHIELD packages installed (in different versions) and/or different DataSHIELD configurations (different options, different R/DataSHIELD packages visibility). All these settings make a "profile" which can be uniquely identified by a name.

• Permissions may apply on these profiles, so that not all profiles can be used by the requesting user (middleware responsibility)
• The profile name may be different from one node to another (additional parameter to login data frame)
• When not specified a default profile name is applied ("default")
• The implementation must be backward compatible, i.e. if the "profile" feature is not implemented by the DS middleware (Opal/Armadillo/DSLite) instance, the R session will still be created (with a warning).
• The profile names can be listed
• The DS config, the installed packages and the R version are listed by profile

The implementation of the profiles will affect the login and administration/monitoring API, not the analysis one (assignments and aggregations apply to the created R server sessions).