Update /users/creator_node route to include non-creator users

[SidSethi]

Description

What is the purpose of this PR? What is the current behavior? New behavior? Relevant links (e.g. Trello) and/or information pertaining to PR?

I found this bug because it broke SnapbackSM, which relies on this route. Specifically, all recurring syncs for non-creator users were broken. This isn't a p0 because majority of users syncs are going through manual sync flow, but still no bueno.

Discprov GET /users/creator_node?creator_node_endpoint=<url> route was not returning data for users that had replica sets but were not creators. Previously this intersection was impossible as we only assigned replica sets after flipping is_creator flag, but recently we changed this in order to assign replica sets to all users on signup to ensure replication of content for all non-creator users.
This bugfix simply replaces the is_creator check in this route with a creator_node_endpoint IS NOT NULL check.

There are similar regressions across the codebase, and separately we need to do comb through and update all references to is_creator.

Tests

List the manual tests and repro instructions to verify that this PR works as anticipated. Include log analysis if possible.
❗ If this change impacts clients, make sure that you have tested the clients ❗

Tested this locally with bugfix, confirming that non-creator users are also returned by this endoint.

❗ Reminder 💡❗:
If this PR touches a critical flow (such as Indexing, Uploads, Gateway or the Filesystem), make sure to add the requires-special-attention label. Add relevant labels as necessary.

[vicky-g]

good find!

[hareeshnagaraj]

LGTM, huge find 💯