Add release notes for 8.0.9 (#7517)

Author: stevejgordon

docs/release-notes/release-notes-8.0.9.asciidoc

@@ -0,0 +1,34 @@
+[[release-notes-8.0.9]]
+== Release notes v8.0.9
+
+[discrete]
+=== Bug fixes
+
+- https://github.com/elastic/elasticsearch-net/pull/7446[#7446] Fix byte properties 
+in index stats types. (issue: https://github.com/elastic/elasticsearch-net/issues/7445[#7445])
+
+[discrete]
+=== Enhancements
+
+- https://github.com/elastic/elasticsearch-net/pull/7467[#7467] Source serialization 
+always sends fractional format for double and floats. (issue: https://github.com/elastic/elasticsearch-net/issues/7051[#7051])
+
+[discrete]
+=== Breaking changes
+
+[discrete]
+==== Source serialization of float and double properties
+
+By default, when serializing `double` and `float` properties, the `System.Text.Json` 
+serializer uses the "G17" format when serializing double types. This format omits 
+the decimal point and/or trailing zeros if they are not required for the data to 
+roundtrip. This is generally correct, as JSON doesn't specify a type for numbers.
+
+However, in the case of source serialization, mappings for numeric properties may 
+be incorrectly inferred if trailing zeros are omitted. In this release, we have 
+included a new custom converter for `float` and `double` types when serialized using
+the default source serializer. These converters ensure that at least one precision 
+digit is included after a decimal point, even for round numbers.
+
+You may therefore observe changes to the serialized source document after 
+upgrading to this version.

docs/release-notes/release-notes.asciidoc

@@ -6,6 +6,7 @@
 [discrete]
 == Version 8.0
 
+* <<release-notes-8.0.9,Release notes v8.0.9>>
 * <<release-notes-8.0.8,Release notes v8.0.8>>
 * <<release-notes-8.0.7,Release notes v8.0.7>>
 * <<release-notes-8.0.6,Release notes v8.0.6>>
@@ -17,6 +18,7 @@
 * <<release-notes-8.0.0,Release notes v8.0.0>>
 
 include::breaking-change-policy.asciidoc[]
+include::release-notes-8.0.9.asciidoc[]
 include::release-notes-8.0.8.asciidoc[]
 include::release-notes-8.0.7.asciidoc[]
 include::release-notes-8.0.6.asciidoc[]