add release notes for 7.5.2 (#51259)

Adds release notes for 7.5.2

Author: Paul Sanwald

docs/reference/release-notes/7.5.asciidoc

@@ -1,16 +1,63 @@
 [[release-notes-7.5.2]]
 == {es} version 7.5.2
 
-coming::[7.5.2]
+[[enhancement-7.5.2]]
+[float]
+=== Enhancements
+
+Features/Ingest::
+* Fork recursive calls in Foreach processor {pull}50514[#50514]
+
+Infra/Core::
+* Fix unintended debug logging in subclasses of TransportMasterNodeAction  {pull}50839[#50839] (issues: {issue}50056[#50056], {issue}50074[#50074], {issue}50076[#50076])
+
 
 [[bug-7.5.2]]
 [float]
 === Bug fixes
 
+Analysis::
+* Fix caching for PreConfiguredTokenFilter {pull}50912[#50912] (issue: {issue}50734[#50734])
+
+CRUD::
+* Block too many concurrent mapping updates {pull}51038[#51038] (issue: {issue}50670[#50670])
+
+Engine::
+* Account soft-deletes in FrozenEngine {pull}51192[#51192] (issue: {issue}50775[#50775])
+
+Features/ILM+SLM::
+* Fix SLM check for restore in progress {pull}50868[#50868]
+
+Features/Ingest::
+* Fix ingest simulate response document order if processor executes async {pull}50244[#50244]
+
+Features/Java Low Level REST Client::
+* Improve warning value extraction performance in response {pull}50208[#50208] (issue: {issue}24114[#24114])
+
 Machine Learning::
 * Fixes potential memory corruption or inconsistent state when background
 persisting categorizer state. {ml-pull}921[#921]
 
+Mapping::
+* Ensure that field collapsing works with field aliases. {pull}50722[#50722] (issues: {issue}32648[#32648], {issue}50121[#50121])
+* Fix meta version of task index mapping {pull}50363[#50363] (issue: {issue}48393[#48393])
+
+Recovery::
+* Check allocation ID when failing shard on recovery {pull}50656[#50656] (issue: {issue}50508[#50508])
+
+SQL::
+* Change the way unsupported data types fields are handled {pull}50823[#50823]
+* Optimization fixes for conjunction merges {pull}50703[#50703] (issue: {issue}49637[#49637])
+*  Fix issue with CAST and NULL checking. {pull}50371[#50371] (issue: {issue}50191[#50191])
+* Fix NPE for JdbcResultSet.getDate(param, Calendar) calls {pull}50184[#50184] (issue: {issue}50174[#50174])
+
+Search::
+* Fix upgrade of custom similarity {pull}50851[#50851] (issue: {issue}50763[#50763])
+
+Security::
+* Always consume the request body of `has_privileges` API {pull}50298[#50298] (issue: {issue}50288[#50288])
+
+
 [[release-notes-7.5.1]]
 == {es} version 7.5.1