Refactor ApprovalRules::UpdateService to support v2 rules

Refactor ApprovalRules::UpdateService to support v2 approval rules.

Used by REST API (PUT) and GraphQL mutations for updating individual approval rules. Currently only supports v1 rules. When v2_approval_rules FF is enabled, should update v2 rules instead.

Critical Issue

GraphQL mutations calling this service will fail with FF on because they try to update v1 rules that don't exist in v2 table.

What

• Check v2_approval_rules feature flag
• Update v2 rules when flag is enabled
• Update v1 rules when flag is disabled