chore: selenium tests to install CLI version fetched from core

[jachro]

This PR changes the behaviour of selenium tests in a way that they call the /api/renku/apiversion API and read the new cli_version property. This way the tests will always use CLI that is compatible (in fact the same) as installed on renku-core.

NOTICE:

• this PR cannot be merged before https://github.com/SwissDataScienceCenter/renku-python/pull/3655 is merged and released
• a following env var definition has to be taken out from the helm-chart/renku/templates/tests/test-renku.yaml; it cannot be done now as it will be brought with https://github.com/SwissDataScienceCenter/renku/pull/3370.

      {{ if .Values.global.renku.cli_version }}
      - name: RENKU_CLI_VERSION
        value: '{{ .Values.global.renku.cli_version }}'
      {{ end }}

/deploy