Add specification for update connector features

[lcawl]

This PR adds a specification to match https://www.elastic.co/guide/en/elasticsearch/reference/master/update-connector-features-api.html

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
connector.check_in	🟢	3/3	3/3
connector.delete	🟢	9/9	9/9
connector.get	🟢	60/60	60/60
connector.last_sync	🟢	7/7	7/7
connector.list	🟢	19/19	19/19
connector.post	🟢	7/7	7/7
connector.put	🟢	14/14	14/14
connector.secret_delete	🟠	Missing type	Missing type
connector.secret_get	🟠	Missing type	Missing type
connector.secret_post	🟠	Missing type	Missing type
connector.secret_put	🟠	Missing type	Missing type
connector.sync_job_cancel	🟢	3/3	3/3
connector.sync_job_check_in	🟠	Missing type	Missing type
connector.sync_job_claim	🟠	Missing type	Missing type
connector.sync_job_delete	🟢	4/4	4/4
connector.sync_job_error	🟠	Missing type	Missing type
connector.sync_job_get	🟢	22/22	22/22
connector.sync_job_list	🟢	12/12	12/12
connector.sync_job_post	🟢	50/50	50/50
connector.sync_job_update_stats	🟠	Missing type	Missing type
connector.update_active_filtering	🟢	1/1	1/1
connector.update_api_key_id	🟢	4/4	4/4
connector.update_configuration	🟢	8/8	8/8
connector.update_error	🟢	4/4	4/4
connector.update_features	🟢	4/4	4/4
connector.update_filtering_validation	🟢	3/3	3/3
connector.update_filtering	🟢	12/12	12/12
connector.update_index_name	🟢	5/5	5/5
connector.update_name	🟢	4/4	4/4
connector.update_native	🟢	3/3	3/3
connector.update_pipeline	🟢	3/3	3/3
connector.update_scheduling	🟢	3/3	3/3
connector.update_service_type	🟢	2/2	2/2
connector.update_status	🟢	3/3	3/3

You can validate these APIs yourself by using the make validate target.

[l-trotta]

LGTM!