Standardize API keys: CamelCase

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
update docs

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)
Merge pull request #6130 from vieux/standardize_api_keys

Standardize api keys to CamelCase