[release-2.1] Drop all capabilities for the webhook server container

[openshift-cherrypick-robot]

This is an automated cherry-pick of #1073

/assign qbarrand

[openshift-ci]

Hi @openshift-cherrypick-robot. Thanks for your PR.

I'm waiting for a rh-ecosystem-edge member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[qbarrand]

/ok-to-test

[qbarrand]

/approve

[openshift-ci]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: openshift-cherrypick-robot, qbarrand

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[yevgeny-shnaidman]

/lgtm