feat: allow filtering of expired CA certs

[dervoeti]

Description

Fixes #625

This PR introduces the ability to filter out expired or soon-to-expire CA certificates from TrustStores and secret volumes by specifying a threshold (a duration, like 1d). If a CA expires within this duration or is already expired it won't be published by secret-operator.
Currently, all CA certificates are published, even expired ones.

Features:

• New caExpiryThreshold field: Added to TrustStore CRD spec to configure minimum remaining CA lifetime
• Volume annotation support: Added secrets.stackable.tech/backend.autotls.ca.expiry-threshold annotation for controlling CA expiry filtering in volumes

If a threshold is not specified, all CAs (including expired ones) are published as before, so this change should be backwards compatible.

I also added a new integration test tls-ca-expiry-threshold for this feature.

CRD change decision: #632

Definition of Done Checklist

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Author

• Changes are OpenShift compatible
• CRD changes approved
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Reviewer

• Code contains useful comments
• Code contains useful logging statements
• (Integration-)Test cases added
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Acceptance

• Feature Tracker has been updated
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