GCS collector Example strings reference a nonexistent --gcs-credentials-path flag

[gaganhr94]

The Example: strings for the GCS collector advertise a --gcs-credentials-path
flag. That flag does not exist — the registered flag is --gcp-credentials-path.

Locations (both at 1e98dab2):

• cmd/guaccollect/cmd/gcs.go:34
• cmd/guacone/cmd/gcs.go:54

Both read:

Example: "guacone collect gcs my-bucket --gcs-credentials-path /secret/sa.json",

Evidence it is wrong:

• pkg/cli/store.go:130 registers gcp-credentials-path.
• The constant two lines above each example is already correct:
  const gcsCredentialsPathFlag = "gcp-credentials-path"
  (cmd/guaccollect/cmd/gcs.go:29, cmd/guacone/cmd/gcs.go:49).
• cmd/guacone/cmd/gcs_test.go:37 asserts the error text
  expected either --gcp-credentials-path flag or GOOGLE_APPLICATION_CREDENTIALS environment variable.

Impact: copying the example from --help fails with unknown flag. The
typo has also propagated into guac-docs (cli-guaccollect.md,
blob-storage.md:59) — tracked as guacsec/guac-docs#237, which will regress if
this is not fixed here too.

Second bug in the same line: the guaccollect example says
guacone collect gcs .... The correct invocation for that binary is
guaccollect gcs ... — guaccollect has no collect subcommand.

Fix: use gcsCredentialsPathFlag's actual value in both examples, and
correct the binary name in the guaccollect one.