Ensure whitespace is stripped off of credentials

Closes #3808 (closed)

Update: Decided to use a helper method and Rubocop cop to ensure we don't handle ENV directly.

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Original description:

• What I changed

  • Credentials - usernames, passwords, tokens, bucket names and region names. Essentially everything that may influence a request/response with a service.
  • GitLab tooling specific env variables that depends on external projects
    • Takeoff related variables
  • VERSION variables that may be used every now and then by developers for testing.

• What I left as is

  • Built-in variables
    • ENV["CI_COMMIT_REF_NAME"]
    • ENV["CI_COMMIT_SHA"]
    • ENV["CI_COMMIT_TAG"]
    • ENV["CI_JOB_NAME"]
    • ENV["CI_JOB_TOKEN"]
    • ENV["CI_JOB_URL"]
    • ENV["CI_PIPELINE_ID"]
    • ENV["CI_PROJECT_DIR"]
    • ENV["CI_PROJECT_ID"]
    • ENV["CI_REGISTRY_IMAGE"]
  • Boolean
    • ENV["ALTERNATIVE_SOURCES"]
    • ENV["COMPILE_ASSETS"]
    • ENV["DISABLE_PUMA_WORKER_KILLER"]
    • ENV["ee"]
    • ENV["NIGHTLY"]
    • ENV["NO_SOURCEMAPS"]
    • ENV["USE_S3_CACHE"]
  • Not commonly updated
    • ENV["BUILDER_IMAGE_REGISTRY"]
    • ENV["BUILDER_IMAGE_REVISION"]
    • ENV["BUILD_LOG_LEVEL"]
    • ENV["CACHE_S3_ACCELERATE"]
    • ENV["DOCKER_TIMEOUT"]
  • Set from other pipelines or by CI
    • ENV["IMAGE_TAG"]
    • ENV["QA_BRANCH"]
    • ENV["TOP_UPSTREAM_SOURCE_JOB"]
    • ENV["TOP_UPSTREAM_SOURCE_PROJECT"]
    • ENV["TOP_UPSTREAM_SOURCE_SHA"]
    • ENV["TRIGGERED_USER"]

PS: I may change my mind about the last three items and add them also to the changed list.