Rename GridFrequency to a more suitable name #770
Description
What's needed?
The name GridFrequency might be confusing as it somehow clashes with the grid connection Grid. or ComponentFrequency would be more suitable
Proposed solution
Rename GridFrequency to a more suitable name like MicrogridFrequency.
Related documentation and tests need to be updated.
Alternatives and workarounds
Alternatively rename it to ACFrequency, because there's only one value for one microgrid, whether it is connected to the grid or not.
Additional context
Originally posted in #758 (review)