feat: Implement new certificate generation service

- Refactor certificate generation into a dedicated service object
- Add Base64 encoding for p12 binary data storage
- Implement serial number generation and storage
- Remove deprecated certificate generation code
- Simplify certificate status checks
- Update certificate controller to use new generator
- Add proper password handling for p12 containers

The main changes include:
- Moving certificate generation logic to CertificateGenerator service
- Proper handling of binary data encoding
- Implementing serial number tracking for future CRL support
- Removing old certificate generation and validation code
- Simplifying the certificate lifecycle management

This commit provides a more maintainable and robust certificate
generation system while preparing for future CRL implementation.

db/migrate/20250313122119_add_serial_and_revoke_states_to_certificates.rb

@@ -0,0 +1,7 @@
+class AddSerialAndRevokeStatesToCertificates < ActiveRecord::Migration[6.1]
+  def change
+    add_column :certificates, :serial, :string, null: true
+    add_column :certificates, :revoked_at, :datetime, null: true
+    add_column :certificates, :revoked_reason, :integer, null: true
+  end
+end