Re-enable webgear-openapi

[rkaippully]

webgear-openapi-1.5.0 was disabled due to build errors. I have uploaded 1.5.1 that fixes these errors.

Checklist:

• Meaningful commit message, eg add my-cool-package (please don't mention build-constraints.yml)
• At least 30 minutes have passed since uploading to Hackage
• If applicable, required system libraries are added to 02-apt-get-install.sh or 03-custom-install.sh
• (recommended) Package have been verified to work with the latest nightly snapshot, e.g by running the verify-package script
• (optional) Package is compatible with the latest version of all dependencies (Run cabal update && cabal outdated)