doc: emphasize Collaborators in GOVERNANCE.md

Put information about Collaborators in GOVERNANCE.md before information
about the CTC. For most things, the CTC is the last place to go, not the
first and Collaborators have a lot of decision-making power in the
project. The governance doc should reflect that.

PR-URL: https://github.com/nodejs/node/pull/13423


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>