This eases adoption of the jobspec package by other projects (e.g. terraform nomad provider, Lavant). Either by consuming directy as a library (hopefully without having go mod import rest of nomad) or by copying the package without modification.
Ideally, this package will be published as an independent module. We aren't ready for that considering we'll be switching to HCLv2 "soon", but eitherway, this seems like a reasonable intermediate step if we choose to.
* jobspec: breakup parse.go into smaller files
* add sidecar_task parsing to jobspec and api
* jobspec: combine service parsing logic for task and group service stanzas
* api: use slice of ConsulUpstream values instead of pointers
