Remove use of "master" in CTSM

We currently have about a thousand instances of the word "master" in CTSM (and about 2k in cime). Most of this is the use of the variable "masterproc". It would be good to get away from this terminology and use a different term in its place. Doing this should be bit-for-bit and relatively straight forward to do. Although because it's used a lot it won't be a trivial thing to do.

Definition of done:
- [ ] Change master branch to main and in documentation #1048
- [ ] Change masterproc/masktask in the code to something else
- [ ] Change comments in code about masterproc from "master" to something else
- [ ] Change use of "master restart" to something else in history handling
- [ ] Change use of "documentation master file" to somehting else
- [ ] Change use of "master input namelist file" to something else
- [ ] Make sure uses of /master/ in documentation for github repos is correct
- [ ] Change use of master clock