Documentation new PR

[jd-lara]

@kdayday @daniel-thom @rodrigomha I merged and opened a new PR because in Github the 50+ comments was making the page super slow to load. I handled most of the comments.

I probably still need to write more for the hydro piece but this is already covering the needed parts in sufficient detail even if we do more changes later.

closes #1213 too

[kdayday]

@jd-lara I can take a look today, but the documentation is currently failing with a set up block error

[jd-lara]

@kdayday the docs build is broken because it requires the newer version of case builder.

[rodrigomha]

Add explanation of level_data_type in HydroReservoirs (Total Volume, Usable Volume, Head and Energy).

[jd-lara]

add explanation for the Buses available field

[m-bossart]

add explanation of new base voltage fields in transformers

[kdayday]

I think this is ready to go once the three recent comments are addressed (reservoir levels, buses available, voltage fields in transformers). I could compile it locally, but still didn't get all the PCSB examples working, so there could still be errors there. I assume some of those are due to the issues in the dev chat yesterday.

I also added links in the new hydro documentation. Please check the hydro how-to to make sure I captured that correctly.

I thinned out the how-to's that are now redundant and reorganized them so hopefully it's a little easier to navigate. Feedback welcome!