backupccl: update default backup telemetry source to ".manual"

This commit updates the telemetry for backup to always include the
source (either ".manual" or ".scheduled"). This allows for folks to
search by a prefix to get the telemetry for all backups, and the
specific source can be appened to filter the telemetry between manual
and scheduled backups.

Release note: None

pkg/ccl/backupccl/backup_planning.go

@@ -887,7 +887,7 @@ func backupPlanHook(
 
  collectTelemetry := func() {
  // sourceSuffix specifies if this schedule was created by a schedule.
- sourceSuffix := ""
+ sourceSuffix := ".manual"
  if backupStmt.CreatedByInfo != nil &&
  backupStmt.CreatedByInfo.Name == jobs.CreatedByScheduledJobs {
  sourceSuffix = ".scheduled"