Rename /integration to /e2etests

[ooq]

Is your feature request related to a problem? Please describe.
Currently, integration tests in Kritis means two things:

1. The integration tests that live inside each individual package. For example, for the containeranalysis package, the integration tests are here.
2. Tests under /integration folder. These tests are run on a GKE cluster to test the end-to-end functionality of Kritis.

When we talk about integration tests, it is easy to confuse the two.

Describe the solution you'd like

I propose to rename the tests in /integration folder as end to end tests, or e2e tests, and rename the folder as so. We probably also want to change the build tag in /integration/run_tests.go to e2e as well.

Describe alternatives you've considered
Do nothing.

Additional context
Add any other context or screenshots about the feature request here.

[ooq]

cc @nenaddedic @aysylu @acamadeo