Write section about software naming in Update Modules chapter

Acceptance criteria:

• A new chapter is created under https://docs.mender.io/2.3/devices/update-modules: "Software versioning", describing:
  • How to let an Update Module version a specific component (--software-name option)
  • How to let an Update Module shadow a different Update Module
    • --software-name '' to shadow the rootfs-image.version entry
    • --software-name NAME to shadow any other software, as in the previous criterion
  • How to let an Update Module describe a different partition using --software-filesystem
  • How to let an Update Module set a specific version of software instead of defaulting to artifact-name, using --software-version

Feature branch name: feature-partial_updates