Enable the devfile registry viewer

[johnmcollier]

What does does this PR do / why we need it:
This PR enables the devfile registry viewer in the devfile registry index server

• Updates the index server dockerfile to build the registry viewer
  • Base image changed to ubi8/nodejs-14-minimal
  • Since we're running the registry viewer under the /viewer endpoint, we have to build the viewer with DEVFILE_VIEWER_ROOT=/viewer
• Index server entrypoint updated to start the node server for the registry viewer, in addition to the index server
• Changes to index server endpoints:
  • /:
    • forwards to /index if no content type requested
    • forwards to/viewer if text/html is requested (i.e. in a browser)
  • /viewer and /viewer/* proxies all requests tolocalhost:3000/viewer
• Helm chart updates:
  • Config map to configure the devfile registry host for the viewer to localhost:8080
  • StartupProbe to verify /viewer is live
  • Slight tweaks to the readiness and liveness probe delays
  • Additional PRs will be needed in the https://github.com/devfile/registry-operator and https://github.com/devfile/registry repositories to update the operator and OpenShift templates with similar changes
• Integration tests in progress

Which issue(s) this PR fixes:

Fixes devfile/api#534

PR acceptance criteria:

• Test (WIP)

• Documentation (WIP)

[johnmcollier]

PRs to update the openshift template and operator (to be merged after this pr is merged):

• OpenShift template: Update OpenShift template for registry viewer registry#63
• Operator: Update the operator to support the registry viewer registry-operator#15

[maysunfaisal]

working as expected

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: GeekArthur, johnmcollier, maysunfaisal

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