Update EPL license to Apache

[kim-tsao]

Which area/kind this issue is related to?

/area api
/area registry

Issue Description

Running a search across our repos show there are still a number of files using the EPL licence. We should update the headers and any boilerplate templates to use the Apache license instead.
Affected repos are:

• api
• registry
• registry-support
• landing-page
• docs
• registry-viewer
• integration-tests
• registry-operator (updates will be made as part of Mechanism to expose a list of devfile registries at a namespace and cluster level #499)

[amisevsk]

I forgot to update the DevWorkspace Operator docs repo at the time: devfile/devworkspace-operator-docs#5