Update release plan for Sync'26 release

[eric-murray]

Problem description
release-plan.yaml needs to be updated by end of the month to signal that device-identifier will participate in the Sync'26 release

Expected action
Update release-plan.yaml after deciding:

• whether to participate and, if so
• whether to only do a minor version update (to 0.4.0) or go for a stable release (1.0.0)

Additional context
See https://lf-camaraproject.atlassian.net/wiki/spaces/CAM/pages/268533761/Sync26+meta-release+ex-Fall26