[STAC-25234] Verify remote_updates default (DD Remote Agent Management) produces no traffic on STS; disable if needed

[kkaempf]

STAC-25234

(Sub-task of [Epic] [STAC-25220] Update main agent from 7.78.2 → 7.80.4 (upstream DataDog Agent 7.79.x + 7.80.x))

Context
DataDog 7.73.0 flipped remote_updates (Remote Agent Management) to default ON (Linux/Windows). In the 7.78.2 rebase ( STAC-24694 Resolved ) our config carries remote_updates=true unoverridden (pkg/config/setup/common_settings.go:989, no [sts] marker), while we force remote_configuration.enabled=false (common_settings.go:1308).

Remote configuration is receiver-incompatible (StackState/SUSE Observability does not run the RC / fleet backend). remote_updates is likely inert without RC, but it is the one receiver-incompatible default in the DD 7.72 -> 7.78 range we did not explicitly pin.

Action

• Confirm whether remote_updates can act independently of remote_configuration.enabled (fleet/installer update polling, DNS, or intake to DD endpoints).
• If it can act independently, add an [sts] false override next to the RC override in common_settings.go.
• Note the new sibling config dir /etc/datadog-agent-exp introduced with this feature; confirm fix_branding.sh coverage / that it is not shipped.

Ref: DD 7.73.0 release notes. Surfaced during the DD 7.72 -> 7.78.2 release-note review.