Add time interpolation to mpc data

[eslickj]

Fixes None

Adds option to linearly interpolate from MPC TimeSeriesData.

Summary/Motivation:

Sometimes you have time series data that doesn't line up perfectly with model time indexes. @blnicho and @jsiirola, this is part of the recent MHE work.

Changes proposed in this PR:

• Add some linear interpolation utility functions and use them to add interpolation capbility to get data and time points not in MPC TimeSeriesData

Legal Acknowledgement

By contributing to this software project, I have read the contribution guide and agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the BSD license.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[Robbybp]

Thanks for the addition. This is definitely functionality we were missing. I think this would be better as it's own interpolate, or get_interpolated_data, method. Would that work for your application?

There is also the question of whether to support some form of interpolation in DynamicModelInterface. (E.g., in get_data_at_time, load_data, or dedicated methods for interpolation.) I'm fine with (and think I prefer) punting for now if you don't need this for your application.