dockerhub release: use org secrets

[jkowalleck]

as of CycloneDX/cyclonedx-node-module#192 (comment)

coderpatros needs to be changed to $DOCKERHUB_USERNAME
$DOCKER_TOKEN needs to be changed to $DOCKERHUB_TOKEN.

Both DOCKERHUB_USERNAME and DOCKERHUB_TOKEN are secrets defined at the GitHub organization level. I assume DOCKER_TOKEN is likely unique to this repo and should be deleted in favor of the organizational secrets.

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tasks

• use the organisation's secrets instead of repos secrets - via gh-action release use org's secrets #272
• remove the repo's secrets via https://github.com/CycloneDX/cyclonedx-python/settings/secrets/actions
  (this requires admin prvilege) via dockerhub release: use org secrets #271 (comment)

[stevespringett]

FYI. These should likely be changed as well.
PYPI_TOKEN (organization)
PYPI_API_TOKEN (repo)

[jkowalleck]

• PYPI_API_TOKEN is not used
• DOCKER_TOKEN was used until gh-action release use org's secrets #272

[jkowalleck]

@stevespringett could you remove unused repo secrets?

• PYPI_API_TOKEN
• DOCKER_TOKEN

[stevespringett]

PYPI_API_TOKEN and DOCKER_TOKEN secrets have been deleted from the repo.