fix: TLS CA cert path used in REQUESTS_CA_BUNDLE

[siegfriedweber]

Description

Fix the TLS CA cert path used in the environment variable REQUESTS_CA_BUNDLE.

The prior implementation always used the static path /stackable/secrets/tls/ca.crt which is not valid for web PKI or SecretClasses other than tls.

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1. Changes are OpenShift compatible
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3. Integration tests passed (for non trivial changes)
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1. Code contains useful comments
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[siegfriedweber]

closed in favor of #530