Make simulation time parameters available via model_params

[mattw-nws]

The simulation start date/time should be made available to running modules, e.g. if a model uses the date or time to compute solar inclination (as Noah-OWP-Modular does--presently it has its own simulation start time in its init config files used for this purpose, and these may disagree). Useful values to make available would probably be:

• simulation_start_epoch
• simulation_timestep
• simulation_start_ordinal_day (1-366)
• simulation_end_epoch (because why not? Or YAGNI?)

Similar to #588, these should probably be specified like this:

{"source":"simulation_time"`, "from": "simulation_timestep"}

Names and "source" name open for discussion.

Current behavior

Expected behavior

Steps to replicate behavior (include URLs)

Screenshots

[PhilMiller]

Given simulation_start_epoch, why can't the rare model that needs simulation_start_ordinal_day calculate it internally?