fix(dashboards): namespace-by-workload multiple matches

[skl]

This PR:

• Fixes multiple series error on network/workload dashboard by adding the missing group_left statement
• Refactors those table column queries to use a single function, instead of duplicating all the PromQL
• Fix make generate target so that it correctly detects dashboard changes
• Ensure cluster label is used in joins, if it exists, where only (namespace,pod) were used previously

Fixes #977