refactor(node-funder): extract label-selector as a flag

[gacevicljubisa]

Refactor: Extract label-selector as a flag with default beekeeper.ethswarm.org/node-funder=true.

• Introduced a flag to specify the label selector for Ingress resources used by node-funder.
• Default label selector set to beekeeper.ethswarm.org/node-funder=true.
• If the label selector is an empty string, no filtering is applied.
• The label selector works in conjunction with the namespace for more granular resource selection.