fix: flag name in documentation

[hardwarefresser]

Hi,

There is a small mistake in the documentation. The flag "fallback-pull-secret" has a wrong name: "fallback-image-pull-secret". Which leads to "Error: unknown flag" when copy+pasted into the flags used to run the service.

See the error here:

time="2024-07-09T12:00:36Z" level=info msg="spawning process: [/usr/local/bin/sbom-operator --dtrack-api-key=[...] --dtrack-base-url=[...] --fallback-image-pull-secret=[...] --format=cyclonedx --targets=dtrack --verbosity=debug]" app=vault-env
Error: unknown flag: --fallback-image-pull-secret
Usage:
  sbom-operator [flags]
[...]
Flags:
  -c, --config string                                 Path to the config-file.
 [...]
      --fallback-pull-secret string                   Fallback-Pull-Secret
[...]

[ckotzbauer]

Thanks for the finding this and this PR!!