Update fields.ecs.yml to ECS v1.5.0 (#16900)

* Update vendored elastic/ecs to v1.5.0

* Update fields.ecs.yml to v1.5.0

* Fix encoding issue in fields' docs

Fields' docs generation is failing in some systems when non-ascii
characters appear in the fields descriptions and/or examples.

* Patch fields.ecs.yml to avoid parser trouble

The fields docs generator was having trouble representing an example as
an object in a way that was consistent across different python3 versions
due to keys in a dict being serialised to string with different
orderings. This caused checks to fail.

NOTICE.txt

@@ -1622,7 +1622,7 @@ Everyone is permitted to copy and distribute copies of this Agreement, but in or
 This Agreement is governed by the laws of the State of New York and the intellectual property laws of the United States of America. No party to this Agreement will bring a legal action under this Agreement more than one year after the cause of action arose. Each party waives its rights to a jury trial in any resulting litigation.
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 Dependency: github.com/elastic/ecs
-Version: v1.4.0
+Version: v1.5.0
 License type (autodetected): Apache-2.0
 ./vendor/github.com/elastic/ecs/LICENSE.txt:
 --------------------------------------------------------------------