update-requirements-yml.sh

- Remove all references to submodules and follow the upstream GitLab
  Cloud Native Chart instead of a special forked repository
- Create a wrapper chart for the Google GKE Marketplace named gitlab-mp
  allowing special configuration unique to the marketplace to be passed
  in without having to change the upstream chart
- Add env-doctor script allowing users to quickly verify that their
  environment is ready to produce a GKE Marketplace update
- Fortify supporting scripts to work when invoked from any path
- Remove deprecated scripts
- Move the Dockerfile definition and build context into the container
  directory and simplify it to use deployer_helm_tiller from Google
  Marketplace Tools
- Insert schema.yaml and requirements.yaml to the build context by
  copying templates rather than running substitutions on the originals
- Support RBAC entries inserted dynamically to the schema.yaml required by
  the Google Marketplace
- Add tooling to build the deployer container, push it and supporting
  containers to the marketplace, and test and tear down the latest
  deployer images
- Tooling is configurable via the environment to avoid the need to alter
  scripts during regular release cycles
- Updated documentation; moved original README to doc/installing and
  split documentation into user versus developer
- Update the .gitlab-ci file to use the new build scripts
- Add script to run Google Marketplace mpdev validation against the
  completed deployer image.

Resolves: https://gitlab.com/charts/gitlab/issues/1041



Signed-off-by: Robert Marshall <rmarshall@gitlab.com>