feat: Support for multiple certificates in the ca-certificates data

[Tomasz-Smelcerz-SAP]

Description:
Currently the runtime-watcher only parses the very first certificate from the ca-certificate(s) data block.
To support the zero-downtime certificate management, it must be able to parse (and use) multiple entries.
A working POC can be used as a reference: Tomasz-Smelcerz-SAP@d7c0f2c

Acceptance Criteria

• Client should be able to support multiple CA certificates from the certificates secret
• Similar implementation to Tomasz-Smelcerz-SAP@d7c0f2c - Logic should be in separate component to parse and add certificates -> Separation of concerns
• Cover with unit test

Related Issues:
kyma-project/lifecycle-manager#1430