Add input for ElectricStorage SOC timeseries

[adfarth]

Added

• Add ElectricStorage input field fixed_soc_series_fraction to allow users to fix the SOC timeseries

Cherry-picked from branch h2-tldrd-mpc by @lixiangk1 with a few small mods

[lixiangk1]

I reviewed the changes and ran some tests and everything seems to make sense. I was wondering if you've noticed in your runs that the cases with the fixed SOC dispatch returns a slightly lower LCC compared to the fixed sizes but unconstrained dispatch? We'd expect it to be slightly higher if results are different right? Is that just a mathematical tolerance thing?