(DOCSP-35060) Perf considerations for multi regions for OM and AppDB (#81)

https://jira.mongodb.org/browse/DOCSP-35060

Adds perf considerations for OM and AppDB, based on discussions in the
MEKO sync document, and then a summary in this [draft
gdoc](https://docs.google.com/document/d/1CFqPCnOsz2gL5kiPeP0sSS9uy2JLFQiWjk80DewGSgg/edit?usp=sharing)
(meeting with @pvertenten on 02/02/2024).
The summary of what to add to this ticket is added to the DOCSP itself.

@pvertenten, thank you for your review! One question I have is: Should
this PR be also applied to Cloud Manager? Asking because the
documentation repos are now different.

[Performance in Multi-Region
Deployments](https://preview-mongodbjuliamongo.gatsbyjs.io/ops-manager/DOCSP-35060/tutorial/configure-application-high-availability/#performance-in-multi-region-deployments)

Latest
[build](https://workerpool-boxgs.mongodbstitch.com/pages/job.html?collName=queue&jobId=65c123786b2f17c95a032dfc)

Author: JuliaMongo

source/tutorial/configure-application-high-availability.txt

@@ -202,6 +202,47 @@ Your |onprem| instance stays in **Upgrade Mode** until all |onprem|
 hosts have been upgraded and restarted. You should not upgrade more
 than one |onprem| host at a time.
 
+.. _opsmgr-multi-regional-perf-considerations:
+
+Performance in Multi-Region Deployments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The geographical distribution of the Application Database and |onprem|
+instances might impact the performance of the |application|.
+
+Multi-region Application Database Performance
++++++++++++++++++++++++++++++++++++++++++++++++
+
+If you plan to replicate the Application Database across multiple regions,
+consider that many of the |onprem| write workload operations use
+``w:2`` :manual:`write concern </reference/write-concern>`, which requires
+acknowledgement from the primary member and one secondary member of the
+replica set for each write operation.
+
+Therefore, having a secondary replica member of the Application Database in
+the **same** region as the primary member can lead to better read and write
+performance.
+
+For example, deploying three Application Database replica set members in
+three regions in a 1-1-1 fashion might result in worse performance
+compared with deploying three Application Database replica members in
+two regions in a 2-1 fashion, where one region hosts two Application Database
+replica set members and another region hosts the third replica set member.
+
+Performance of the |mms| UI
++++++++++++++++++++++++++++++++++++
+
+The |mms| UI is more performant if you connect to the |application| instance
+deployed it in the same region as the Application Database primary member
+of the Application Database replica set.
+
+In other words, you may achieve a better user experience connecting to
+the |application| instance hosted in the same region as the
+Application Database primary member of the replica set, rather than
+connecting to a closer |application| instance where the instance itself
+must connect to a primary Application Database replica set member hosted in
+a different, distant region with a high latency.
+
 Prerequisites
 -------------