Add exponential backoff to orbit enroll retries (#17368)

#16594

- [X] Changes file added for user-visible changes in `changes/` or
`orbit/changes/`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [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)).

server/service/orbit_client.go

@@ -302,8 +302,12 @@ func (oc *OrbitClient) getNodeKeyOrEnroll() (string, error) {
 				return err
 			}
 		},
-		retry.WithInterval(OrbitRetryInterval()),
+		// The below configuration means the following retry intervals (exponential backoff):
+		// 10s, 20s, 40s, 80s, 160s and then return the failure (max attempts = 6)
+		// thus executing no more than ~6 enroll request failures every ~5 minutes.
+		retry.WithInterval(orbitEnrollRetryInterval()),
 		retry.WithMaxAttempts(constant.OrbitEnrollMaxRetries),
+		retry.WithBackoffMultiplier(constant.OrbitEnrollBackoffMultiplier),
 	); err != nil {
 		return "", fmt.Errorf("orbit node key enroll failed, attempts=%d", constant.OrbitEnrollMaxRetries)
 	}
@@ -402,7 +406,7 @@ func (oc *OrbitClient) setLastRecordedError(err error) {
 	oc.lastRecordedErr = fmt.Errorf("%s: %w", time.Now().UTC().Format("2006-01-02T15:04:05Z"), err)
 }
 
-func OrbitRetryInterval() time.Duration {
+func orbitEnrollRetryInterval() time.Duration {
 	interval := os.Getenv("FLEETD_ENROLL_RETRY_INTERVAL")
 	if interval != "" {
 		d, err := time.ParseDuration(interval)