96414 Add submit_appointment method to EPS AppointmentService

[randomsync]

Summary

Implements a new method to submit appointments to the EPS API using the /appointments/{appointmentId}/submit endpoint. The method:

• Validates appointment_id and required parameters (network_id, provider_service_id,
  slot_ids, referral_number)
• Supports optional additional_patient_attributes
• Returns API response wrapped in OpenStruct

Related issue(s)

department-of-veterans-affairs/va.gov-team#96414

Testing done

• New code is covered by unit tests

What areas of the site does it impact?

VAOS appointments, community care referrals

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs

[kanchanasuriya]

Can we please also handle the scenario of network_id or other mandatory parameters being nil or empty?

[randomsync]

IMHO that is unnecessary and if it is being called by the caller without those checks, the error message from underlying service should be returned. Please also see the patterns in other service methods.