Use existing session information instead of running the analysis to match the user's environment

[nuest]

The current packaging mechanism executes the analysis to capture the runtime, which naturally differs from the one the user created. containerit can already create a Dockerfile for a given sessionInfo, which would also be a lot faster

• check if a sessionInfo.RData (which may only contain only one object of class sessionInfo (restriction necessary?)) file in the workspace/ERC exists and use it to create the manifest

Alternatives

• expose the base language version as part of the metadata form, i.e. R, so that a user can indirectly choose the base image version created in the manifest generation