Switch sippy to GKE managed certificate

[ameukam]

Ref: #1943

Signed-off-by: Arnaud Meukam ameukam@gmail.com

[k8s-ci-robot]

Skipping CI for Draft Pull Request.
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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ameukam

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[wojtek-t]

/lgtm

Thanks!

[ameukam]

Certificate sucessfully deployed:

openssl s_client -connect sippy.k8s.io:443
CONNECTED(00000003)
depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = sippy.k8s.io
verify return:1

https://ssllabs.com/ssltest/analyze.html?d=sippy.k8s.io

[ameukam]

xref: #1900