Draft: Resolve "Initial sampling for multitrajectory DFT"

Description

Implement the framework for passing initial conditions to the replicas of an ensemble.

Please note, that this is still a VERY early draft, mainly to test and discuss the best strategy to implement the initial conditions.

News snippet

Implement the framework for passing initial conditions to the replicas of an ensemble.

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.

Closes #959