Add support for profiling Flexmeasures

[Nischay-Pro]

Currently, Flexmeasures has no support for profiling. This makes it difficult to identify and analyze performance bottlenecks in the code as the application matures.

Some proposed solutions are

1. Integrate pyinstrument in Makefile:
   Integrate pyinstrument into the Makefile allowing the developer to call make with appropriate commands to start flexmeasures with profiler attached.
   A possible target in Makefile can be make run-profiler
   This calls the profiler which in turn starts flexmeasures. Can be run to profile the entire application.

2. Integrate pyinstrument as a part of the pytest suite or CI:
   Integrate the profiler to benchmark and profile critical parts of the code and automatically generate profile reports which can be quickly viewed by the developer to check the impact on performance.

[nhoening]

Closing this as #722 enable us to use it. Not sure if we ever want the pytest integration, as well.