**Related issue:** Resolves#47699
## Testing
- [x] QA'd all new/changed functionality manually
## What & why
Entra conditional access is becoming available to self-hosted Fleet
Premium instances, which don't have the shared `MS-API-KEY` that
cloud-managed customers use. This makes the `microsoft-proxy/*`
endpoints reachable without that key by dropping the `is-cloud-customer`
policy gate (and the now-unused shared-secret config comments / policy
file).
A replacement auth mechanism for the proxy is tracked separately in
#47702.
> Split out of #49414 so the website change can ship independently.
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## Summary by CodeRabbit
* **Security / Access Control**
* Updated Microsoft proxy access handling to bypass the prior
cloud-customer check for matching requests.
* **Configuration**
* Removed unused cloud-customer compliance proxy shared-secret settings.
* **Bug Fixes**
* Improved compliance partner tenant creation by detecting existing
tenants using the provided Entra tenant ID and corrected the success
message text.
* **Data Model**
* Removed uniqueness enforcement for stored fleet instance URLs to
prevent avoidable conflicts.
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Co-authored-by: Eric <eashaw@sailsjs.com>
