Add RAG to terms and vale (opensearch-project#9136)

* Add RAG to terms and vale

Signed-off-by: natebower <[email protected]>

* Update .github/vale/styles/OpenSearch/SubstitutionsError.yml

Co-authored-by: kolchfa-aws <[email protected]>
Signed-off-by: Nathan Bower <[email protected]>

---------

Signed-off-by: natebower <[email protected]>
Signed-off-by: Nathan Bower <[email protected]>
Co-authored-by: kolchfa-aws <[email protected]>

Author: natebower

.github/vale/styles/OpenSearch/SubstitutionsError.yml

@@ -37,6 +37,7 @@ swap:
   'pre-trained': pretrained
   'premigration': pre-migration
   're-enable': reenable
+  'retrieval augmented generation': retrieval-augmented generation
   'screen shot': screenshot
   'sample request': example request
   'sample response': example response

TERMS.md

@@ -654,6 +654,8 @@ Copy of a primary shard. Helps improve performance when using indexes across mul
 
 Use as a synonym for repository, on second and subsequent use.
 
+**retrieval-augmented generation (RAG)**
+
 **RPM Package Manager (RPM)**
 
 Formerly known as RedHat Package Manager. An open-source package management system for use with Linux distributions.