Introduce a freespace balancing strategy

This set of commits implement a new groupbalancer strategy that tries to balance groups towards equal value of freespace per group. In order to avoid jitters, we set a (configurable) range of +-2% on the calculated value as the value beyond which a group is selected for balancing.

Fixes: EOS-5803

added 8 commits

• 19502002 - 1 commit from branch master
• 4ca92166 - COMMON: StringSplit add support for set types
• e6e5f2d3 - UNIT_TESTS: Groupbalancer: Add tests for extract value
• a63cb8d3 - MGM: GroupBalancerUtils: make the map value extractor generic
• 42ad01c6 - MGM: GroupBalancerUtils: introduce a commalist extractor
• 44628786 - MGM: GroupBalancer: introduce a freespace engine
• b2b0f5fb - MGM: GroupBalancer: immediately apply group blocklisting
• 6bca5e9a - CONSOLE: fix formatting in some space options

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merged