Create a dedicated object that compares two grids

# :rocket:

- [ ] Is your feature request essential for your project?

### Describe the workflow you want to enable
Now that we have grid objects whose number of attributes and the shape of the attributes can vary from one grid model to another or even among the same grid model (e.g. extra column in `bus` data frame for demand flexibility, etc), the simple overwriting of `__eq__` is not enough anymore.

### Describe your proposed implementation, if applicable
* Create a `CompareGrid` class living in a new `powersimdata.input.compare_grid` module
* The constructor takes two `Grid` objects
* Define multiple methods that compare individual portion of the `Grid` objects, e.g., `compare_branch()`. The function would have several parameters such as: `columns` that would define a list of columns to compare, `tol` that would define the tolerance on the comparison. Each methods would perform an assertion
* Remove the overwriting of `__eq__` in `powersimdata.input.grid`

### Additional context
Some tests would need to be refactored