Upgrade to knative 0.8.1

What does this MR do?

Update the version of Knative used from 0.7 -> 0.8.1.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

This is a backend update only which requires no browser verification. Smoke tests were performed by verifying the update of the chart against a GCE instance. Tests were updated to include the new version.

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

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