Add code coverage reporting into `make e2e`

[m1kola]

With Go 1.20 we can now build binaries for e2e which can produce coverage reports (see go build -cover).

We eventually want to combine e2e coverage reports with unit test coverage (see #276) to get a better visibility into combined test coverage.

Acceptance criteria:

• make e2e builds a coverage-instrumented binary as part of e2e test and generates coverage report
• It extracts code coverage reports from the e2e cluster
• Converts binary reports into -coverprofile text format or any other accepted format of the code coverage solution decided in Add integration with code coverage reporting solution #276

Useful links:

• https://go.dev/blog/integration-test-coverage
• https://go.dev/testing/coverage/

[m1kola]

Done via #284