feat: support PKCS#8

[livio-a]

Until now BytesToPrivateKey was only able to handle PKCS#1 RSA keys. This PR adds support for the PKCS#8 format including RSA, ECDSA or ED25519 private keys. These keys are used for the signing of JWT, e.g. JWT Profile assertions.

required for https://github.com/zitadel/zitadel-tools/issues/97

Definition of Ready

• [x] I am happy with the code
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• [x] Where possible E2E tests are implemented
• [x] Documentation/examples are up-to-date
• [x] All non-functional requirements are met
• [x] Functionality of the acceptance criteria is checked manually on the dev system.

[github-actions[bot]]

:tada: This PR is included in version 3.26.0 :tada:

The release is available on GitHub release

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