Document registrant-changes endpoints

[juankuquintana]

This PR introduces a new documentation page for registrant-changes API endpoints.

Fixes #894

🔍 QA

• Verify the documentation is shown upon running the project
• The API can also be verified by running tests against it

# Get registrant changes
curl -H 'Authorization: Bearer dnsimpletest-api-key' \
     -H 'Accept: application/json' \
     -H "Content-Type: application/json" \
     -X GET \
     -d '{"state":"completed","domain_id":"<domain_name>"}' \
     https://api.sandbox.dnsimple.com/v2/<account_id>/registrar/registrant_changes

# Create registrant change
curl -H 'Authorization: Bearer dnsimpletest-api-key' \
     -H 'Accept: application/json' \
     -H "Content-Type: application/json" \
     -X POST \
     -d '{"contact_id":<contact_id>,"domain_id":"<domain_name>"}' \
     https://api.sandbox.dnsimple.com/v2/<account_id>/registrar/registrant_changes

# Check registrant change
curl -H 'Authorization: Bearer dnsimpletest-api-key' \
     -H 'Accept: application/json' \
     -H "Content-Type: application/json" \
     -X POST \
     -d '{"contact_id":<contact_id>,"domain_id":"registeradomaintforteste.com"}' \
     https://api.sandbox.dnsimple.com/v2/<account_id>/registrar/registrant_changes/check

# Get registrant change
curl -H 'Authorization: Bearer dnsimpletest-api-key' \
     -H 'Accept: application/json' \
     -H "Content-Type: application/json" \
     -X GET \
     https://api.sandbox.dnsimple.com/v2/<account_id>/registrar/registrant_changes/<registrant_change_id>

# Delete registrant change
curl -H 'Authorization: Bearer dnsimpletest-api-key' \
     -H 'Accept: application/json' \
     -H "Content-Type: application/json" \
     -X DELETE \
     https://api.sandbox.dnsimple.com/v2/<account_id>/registrar/registrant_changes/<registrant_change_id>

📋 Deployment Pre/Post tasks

Deployment Verification

• QAd

[juankuquintana]

While working on this, I also noticed that this endpoints are being used currently by customers, this can be seen on our DD logs.

[aeden]

https://github.com/dnsimple/dnsimple-developer/pull/895/files#diff-acb3aa7e874a0877690713ea6cf11d484e41833e1c2f4112f0170a802c1e3d9bR11-R15 seems to say two different things: "change the registrant contact for a registered domain" and then in the info "Registrant changes allow you update the registrant information for a domain". I believe the info statement muddies the intent of the API rather than clarifies it, assuming that this endpoint behaves as I expect, which is to change the registrant contact from one contact to another.

[juankuquintana]

https://github.com/dnsimple/dnsimple-developer/pull/895/files#diff-acb3aa7e874a0877690713ea6cf11d484e41833e1c2f4112f0170a802c1e3d9bR11-R15 seems to say two different things: "change the registrant contact for a registered domain" and then in the info "Registrant changes allow you update the registrant information for a domain". I believe the info statement muddies the intent of the API rather than clarifies it, assuming that this endpoint behaves as I expect, which is to change the registrant contact from one contact to another.

@aeden may I get another look?