feat: wider scopes for startup CPU boost

[mikouaj]

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Description

Introduce two new startup CPU boosts types as proposed in #55 and #56

• ClusterStartupCPUBoost - cluster wide startup CPU boost that matches PODs across all of the namespaces with a given selector
• NamespaceStartupCPUBoost - namespace'd startup CPU boost that matches all of the PODs within the given namespace

The POD should be matched against the startup CPU boost with most specific scope.
StartupCPUBoost -- no-match --> NamespaceStartupCPUBoost -- no-match --> ClusterStartupCPUBoost

Tasks:

• Decouple common / core startup CPU boost logic from the implementation
• Implement NamespaceStartupCPUBoost
• Implement ClusterStartupCPUBoost

References

• Global CPUBoost #55
• Multiple StartupCPUBoosts targeting same pod #56