Added deduplication to unmanaged core modules listing

[musztardem]

Description

Changes proposed in this pull request:

• The duplication was occurring when the unmanaged module was also missing in the Kyma CR.
• In such situation we were iterating over the module templates available on the cluster and verifying if their module manager is running.
• Since there were multiple versions of the same module among module templates, the CLI was finding duplicated manager entries (e.g. serverless-1.7.4 and serverless-1.8.1 have the same manager definitions in their module templates.)
• The module version is later extracted from the data gathered from the running instance of the manager - hence the duplication.

Related issue(s)

#2567