Add release notes for elastic/kibana#191730 (#1292) (#1293)

(cherry picked from commit 4928797)

Co-authored-by: Jaime Soriano Pastor <[email protected]>

docs/en/ingest-management/release-notes/release-notes-8.15.asciidoc

@@ -34,12 +34,36 @@ Review important information about the {fleet} and {agent} 8.15.1 release.
 
 {fleet}::
 * Remove duplicative retries from client-side requests to APIs that depend on EPR ({kibana-pull}190722[#190722]).
+* Add mappings for properties of nested objects that were previously omitted ({kibana-pull}191730[#191730]).
 
 {agent}::
 * Fix the Debian packaging to properly copy the `state.enc` and `state.yml` files to the new version of the {agent}. {agent-pull}5260[#5260] {agent-issue}5101[#5101]
 * Switch from wall clock to montonic clocks for component check-in calculation. {agent-pull}5284[#5284] {agent-issue}5277[#5277]
 * For a failed installation, return a `nil` error instead of `syscall.Errno(0)` which indicates a successful operation on Windows. {agent-pull}5317[#5317] {agent-issue}4496[#4496]
 
+[discrete]
+[[known-issues-8.15.1]]
+=== Known issues
+
+[[known-issue-issue-191730]]
+.Fleet configures additional properties in some nested objects in index templates of integrations.
+[%collapsible]
+====
+
+*Details*
+
+A bugfix intended to be released in 8.16.0 was also included in 8.15.1. It fixes
+an actual issue where some mappings were not being generated, but this also
+includes additional mappings when installing some integrations in 8.15.1 that
+were not included when using 8.15.0.
+
+*Impact* +
+
+Users may notice that some index templates include additional mappings for the
+same package versions.
+
+====
+
 // end 8.15.1 relnotes
 
 // begin 8.15.0 relnotes