Add data stream descriptions

[lcawl]

This PR adds descriptions from:

• https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-get-data-stream.html
• https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-delete-data-stream.html
• https://www.elastic.co/guide/en/elasticsearch/reference/master/indices-create-data-stream.html

NOTE: In addition to adding descriptions in specification/indices/_types/DataStream.ts, I've sorted the properties alphabetically so they show up nicely in our output.

[abdonpijpelink]

LGTM. Added a question.

[github-actions]

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

API	Status	Request	Response
indices.add_block	🟢	2/2	2/2
indices.analyze	🟢	20/20	20/20
indices.clear_cache	🟢	4/4	4/4
indices.clone	🟢	6/6	6/6
indices.close	🟢	42/42	42/42
indices.create_data_stream	🟢	25/25	25/25
indices.create	🔴	673/679	679/679
indices.data_streams_stats	🟢	4/4	4/4
indices.delete_alias	🟢	15/15	15/15
indices.delete_data_lifecycle	⚪	Missing test	Missing test
indices.delete_data_stream	🟢	27/27	27/27
indices.delete_index_template	🟢	1/1	1/1
indices.delete_template	🟢	9/9	9/9
indices.delete	🟢	104/104	104/104
indices.disk_usage	🟢	1/1	1/1
indices.downsample	⚪	Missing test	Missing test
indices.exists_alias	🟢	36/36	36/36
indices.exists_index_template	⚪	Missing test	Missing test
indices.exists_template	🟢	15/15	15/15
indices.exists	🟢	39/39	39/39
indices.explain_data_lifecycle	⚪	Missing test	Missing test
indices.field_usage_stats	🟢	5/5	5/5
indices.flush	🟢	9/9	9/9
indices.forcemerge	🔴	4/4	3/4
indices.get_alias	🔴	80/80	68/80
indices.get_data_lifecycle	⚪	Missing test	Missing test
indices.get_data_stream	🟢	12/12	12/12
indices.get_field_mapping	🔴	15/15	14/15
indices.get_index_template	🔴	16/16	14/16
indices.get_mapping	🟢	74/74	74/74
indices.get_settings	🔴	54/54	50/54
indices.get_template	🟢	30/30	30/30
indices.get	🟢	52/52	52/52
indices.migrate_to_data_stream	⚪	Missing test	Missing test
indices.modify_data_stream	⚪	Missing test	Missing test
indices.open	🟢	17/17	17/17
indices.promote_data_stream	⚪	Missing test	Missing test
indices.put_alias	🟢	54/54	54/54
indices.put_data_lifecycle	⚪	Missing test	Missing test
indices.put_index_template	🔴	36/37	37/37
indices.put_mapping	🔴	70/71	71/71
indices.put_settings	🔴	46/48	48/48
indices.put_template	🔴	39/41	41/41
indices.recovery	🟢	11/11	11/11
indices.refresh	🟢	202/202	202/202
indices.reload_search_analyzers	🟢	2/2	2/2
indices.resolve_index	🟢	5/5	5/5
indices.rollover	🟢	14/14	14/14
indices.segments	🔴	6/6	5/6
indices.shard_stores	🔴	5/5	4/5
indices.shrink	🟢	5/5	5/5
indices.simulate_index_template	🟢	4/4	4/4
indices.simulate_template	🟢	4/4	4/4
indices.split	🟢	4/4	4/4
indices.stats	🟢	82/82	81/81
indices.unfreeze	🟢	1/1	1/1
indices.update_aliases	🟢	22/22	22/22
indices.validate_query	🟢	7/7	7/7

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