Resolve "[ADD] Allow Node Operator to set custom fee for pooled validators"

Related to #1309 (closed)

• Adds ability for Node Operator to set their operator fee (0-10000 basis points).
• Proposed rules for updating operator fee:
  • Operator can set fee to whatever if no outside provider has bonded
  • Operator can only decrease fee if an outside provider has bonded
• Removed setting operator fee to default in refundBond and in bond handler - a store migration will set operator fee to default in 1.87 release, then operators should handle setting the fee themselves