Reducing the number of fleetd calls to fleet/orbit/config endpoint by
caching the config for 3 seconds.
#15541
# Checklist for submitter
- [x] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
- [x] Added/updated tests
- [x] Manual QA for all new/changed functionality
- For Orbit and Fleet Desktop changes:
- [x] Manual QA must be performed in the three main OSs, macOS, Windows
and Linux.
- [x] Auto-update manual QA, from released version of component to new
version (see [tools/tuf/test](../tools/tuf/test/README.md)).
