Add configurable counterfeit plugin to evaluate optimizer scalability

[sekruse]

In order to evaluate the optimizer scalability w.r.t. the number Platforms/Plugins registered with Rheem, this issue proposes to introduce a configurable counterfeit Plugin.

There are two components of the optimizer that are particularly susceptible to the number of Platforms:

1. The plan enumeration component likely declines in performance as there are more alternative plans to consider. This is particularly governed by the number of alternatives for each Rheem operator.
2. The data movement planning is likely affected by the size and density of the ChannelConversionGraph.

Now the main idea of the counterfeit plugin is to add one or more Platforms to the RheemContext, thereby providing new OperatorMappings and new ChannelConversions. This should be done in a configurable manner.