fix(cli): List mongodb storages returns empty result

[Benjosh95]

Description

The issue is that the condition len(*options.Storages.Storages.StorageClasses) == 0 is incorrect - it's actually preventing the table from being displayed when there are storage classes available. It should be checking if the length is greater than 0, not equal to 0.

Jira-Ticket: stackitcli-200

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see e.g. here)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)

Testing-Instructions

$ stackit mongodbflex options --flavor-id 1.2 --storages
returning a table with the requested content.

[rubenhoenle]

• Fix also the postgres option before merge: fix(cli): List mongodb storages returns empty result  #778 (comment)