[DOCS] Edit licensing API summaries

[lcawl]

Relates to #3226

This PR edits the summaries and descriptions in https://www.elastic.co/docs/api/doc/elasticsearch/group/endpoint-license based on information from https://www.elastic.co/guide/en/elasticsearch/reference/master/licensing-apis.html

[github-actions]

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

API	Status	Request	Response
license.delete	🟢	3/3	3/3
license.get_basic_status	🟢	3/3	3/3
license.get_trial_status	🟢	3/3	3/3
license.get	🟢	6/6	6/6
license.post_start_basic	🟢	5/5	5/5
license.post_start_trial	🟢	2/2	2/2
license.post	🟢	1/1	1/1

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

[marciw]

LGTM!