Reword Collaborator as Member

[legendecas]

In the moderation policy, the term "Collaborator" actually refers to any individual with configured triage role or higher in any Node.js GitHub organization repository, but not the well-known term in Node.js that refers to who has write access to a certain repo like https://github.com/nodejs/node.

This updates the Moderation-Policy.md to disambiguate the term from the "Collaborator" that's commonly used in the context of Node.js org.

/cc @nodejs/moderation @nodejs/tsc