Add 'health' warning for 2300 projections

Include a flag, which is output to the user's terminal if a `projection_end_year` is set between 2100 and 2300, indicating that the methods for the 2300 projections are different from that of the 2100 projections.

Include a reference to @mo-MattPalmer Palmer et. al (2020) for further details.

Locate where projection_end_year is parsed and where messages are written to the user's terminal. Add a warning for values between 2100 and 2300, including the distinction between the 2300 and 2100 projection methods and a reference to Palmer et al. (2020); verify the warning appears only for that range.

Written by the indexing model from the issue text.