fix: check if external.hostname is empty to not set an invalid value to the certificate

[aaronschweig]

Summary

What Type of PR Is This?

/kind bug

Related Issue(s)

Currently, if the .spec.external.hostname of a FrontProxy resource is empty, it just gets set on the created certificate, which will result in a tls error, when trying interact with that proxy through a go client. kubectl does not complain, but a golang client will complain about an invalid dnsName attributes inside the server certificate.

Release Notes

NONE

[kcp-ci-bot]

Hi @aaronschweig. Thanks for your PR.

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[mjudeikis]

/lgtm
/approve

[kcp-ci-bot]

LGTM label has been added.

Git tree hash: 055b9cec245bcc93bb678924f400d0643114fd11

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mjudeikis

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