Realtime analysis output failing when output has no subdirectory

[ijpulidos]

In #561 the realtime analysis file was introduced but the path for it did not account for simulations where the results are to be generated in the same current owrking directory, resulting in the wrong path and a PermissionError like the following, when trying to write the yaml file.

PermissionError: [Errno 13] Permission denied: '/alanine_dipeptide_legacy_real_time_analysis.yaml'

This can be solved by using os.path.join instead of f-strings when dealing with paths.