[Docs]: Update Contributing documentation

[ryanmerolle]

ISSUE TYPE

• Documentation update

SUMMARY

Contributing documentation should include updated instructions on:

• How to locally test your PR using ansible-test (several variations)
• How to locally test your PR by installing with ansible-galaxy collection install -f git+https://.com/<user>/ansible_modules.git,<branch>
• How to auto update the documentation using antsibull-docs collection --use-current --squash-hierarchy --dest-dir docs/plugins/ netbox.netbox