Added CHANGELOG and fixed phpstan JsonException issue for php < 7.3

Author: ezimuel

CHANGELOG.md

@@ -1,3 +1,12 @@
+## Release 7.8.0
+
+- Updated endpoints and namespaces for Elasticsearch 7.8
+  [f2a0828](https://github.com/elastic/elasticsearch-php/commit/f2a0828d5ee9d126ad63e2a1d43f70b4013845e2)
+- Improved documentation
+  [#1038](https://github.com/elastic/elasticsearch-php/pull/1038)
+  [#1027](https://github.com/elastic/elasticsearch-php/pull/1027)
+  [#1025](https://github.com/elastic/elasticsearch-php/pull/1025)
+
 ## Release 7.7.0
 
 - Removed setId() into endpoints, fixed `util/GenerateEndpoints.php`

phpstan.neon

@@ -2,3 +2,6 @@ parameters:
     ignoreErrors:
         - '#Unsafe usage of new static()#'
         - '#Call to static method performRequest\(\) on trait#'
+        - '#Constant JSON_THROW_ON_ERROR not found#'
+        - '#Caught class JsonException not found#'
+        - '#Call to method getCode\(\) on an unknown class JsonException#'