DOCSP-45776 backpors DOCSP-44307 Remove OM version from the login page (#480) (#574)

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- [DOCSP-45776](https://jira.mongodb.org/browse/DOCSP-45776) 
-
[STAGING](https://deploy-preview-574--10gen-docs-ops-manager.netlify.app/reference/configuration/)

### Self-Review Checklist

- [ ]
[Define](https://wiki.corp.mongodb.com/display/DE/Taxonomy+tagging+instructions)
taxonomy
[values](https://wiki.corp.mongodb.com/display/DE/Docs+Taxonomy) at top
of page.
- [ ] Add genre facets (tutorial or reference), as in this [example
PR](10gen/cloud-docs#5042).
- [ ] Add programmingLanguage (if necessary).
- [ ] Add meta keywords (if necessary).
- [ ] Resolve any new warnings or errors in the build.
- [ ] Proofread for spelling and grammatical errors.
- [ ] Check staging for rendering issues.
- [ ] Confirm links are working.

Author: kanchana-mongodb

source/includes/setting-fileConf-mms.security.show.om.version.rst

@@ -0,0 +1,9 @@
+.. setting:: mms.security.show.om.version
+
+   *Type*: boolean
+
+   *Default*: True
+   
+   When ``false``, |mms| doesn't display the version number in the login
+   page.
+   

source/reference/configuration.txt

@@ -269,6 +269,7 @@ Security
 
 .. include:: /includes/setting-fileConf-mms.security.disableBrowserCaching.rst
 .. include:: /includes/setting-fileConf-mms.security.hstsMaxAgeSeconds.rst
+.. include:: //includes/setting-fileConf-mms.security.show.om.version.rst
 
 Non-Uniform Memory Access (NUMA)
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~