feat: Implement P12 certificate generation improvements

- Replace hardcoded P12 password with randomly generated one
- Add p12_password column to certificates table
- Update certificate serializer to include p12 password in response
- Remove deprecated certificate revocation logic
- Add tests for certificate revocation functionality
- Implement async P12 generation via Sidekiq job
- Add job uniqueness to prevent parallel certificate generation

Migration changes:
- Replace p12_password_digest with p12_password column
- Add safety measures for column removal

lib/serializers/repp/certificate.rb

@@ -79,7 +79,8 @@ module Serializers
       def p12_data(obj)
         {
           body: obj.p12,
-          type: 'PKCS12'
+          type: 'PKCS12',
+          password: obj.p12_password
         }
       end