Bump version of knative from 0.3 -> 0.5

What does this MR do?

Update the version of Knative Serving to install from 0.3 -> 0.5.

For release notes covering the differences:

• Serving: https://github.com/knative/serving/releases/tag/v0.5.0

Note: There is a merge request open for the ee branch: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/10662

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

Testing consisted of bringing up a Kubernetes cluster with Knative, starting a knative service, and verifying the the serverless screen and detailed views. The rspec for the knative model had to be adjusted to account for the version bump as well.

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team