Add river sockeye spawning/rearing model

[smnorris]

Model criteria / timeline / priority level all TBD.

From PSF:

We do identify the spawning that we consider to represent river sockeye vs. lake sockeye spawning within our PSE, but using our defined lake sockeye upstream ZOIs, and then assuming all observed downstream spawning is river sockeye spawning. Rearing areas become difficult to identify, but I’m sure we could work to identify some acceptable rule set around that as well down the road as for the other species.