Add extra manifests

[amine7777]

This pull request introduces the capability to deploy additional Kubernetes manifests, such as External Secrets, using the Helm chart's extraManifests value. By leveraging this enhancement, users can now dynamically include custom manifests alongside the chart deployment, ensuring greater flexibility and streamlined resource management.

• Added templating logic to support .Values.extraManifests for including custom YAML manifests.
• Ensured proper YAML formatting with separators (---) for each additional manifest.

Definition of Ready

• I am happy with the code
• Short description of the feature/issue is added in the pr description
• PR is linked to the corresponding user story
• Acceptance criteria are met
• All open todos and follow ups are defined in a new ticket and justified
• Deviations from the acceptance criteria and design are agreed with the PO and documented.
• No debug or dead code
• My code has no repetitions
• Documentation/examples are up-to-date
• All non-functional requirements are met
• If possible, the test configuration is adjusted so acceptance tests cover my changes

[fforootd]

Thanks for this PR!

CC @eliobischof