Model refactor: rename EligibilityVerifier to EnrollmentFlow

[thekaveman]

Acceptance criteria

• A new model exists called EnrollmentFlow
• Each field in the model definition has a description
• Fields from EligibilityVerifier are moved and renamed:

    display_order = models.PositiveSmallIntegerField(default=0, blank=False, null=False)
    help_template = models.TextField(null=True, blank=True)
    selection_label_template = models.TextField()
    eligibility_start_template = models.TextField(null=True, blank=True)
    eligibility_unverified_template = models.TextField(null=True, blank=True)
    eligibility_form_class = models.TextField(null=True, blank=True)
    eligibility_api_url = models.TextField(null=True, blank=True)
    eligibility_api_auth_header = models.TextField(null=True, blank=True)
    eligibility_api_auth_key_secret_name = SecretNameField(null=True, blank=True)
    eligibility_api_public_key = models.ForeignKey(PemData, related_name="+", on_delete=models.PROTECT, null=True, blank=True)
    eligibility_api_jwe_cek_enc = models.TextField(null=True, blank=True)
    eligibility_api_jwe_encryption_alg = models.TextField(null=True, blank=True)
    eligibility_api_jws_signing_alg = models.TextField(null=True, blank=True)
    claims_provider = models.ForeignKey(ClaimsProvider, on_delete=models.PROTECT, null=True, blank=True)
    claims_scope = models.TextField(null=True, blank=True)
    claims_claim = models.TextField(null=True, blank=True)
    claims_scheme = models.TextField()

• active field from EligibilityVerifier is dropped and not used on EnrollmentFlow
• The model for EligibilityVerifier no longer exists
• TransitAgency.eligibility_verifiers field renamed to TransitAgency.enrollment_flows
• View permissions updated for the new model
• Edit permissions updated for the new model
• EligibilityVerifier field exclusions moved to the new model
• EligibilityVerifier read-only fields moved to the new model

Impact on existing data

• Standard migrations for model/field renames should maintain existing data (including for TransitAgency.eligibility_verifiers --> TransitAgency.enrollment_flows)