Fix: Add MDB_MEMBERS again (#593)

# Summary

An env var from enterprise search snippets was accidentally removed. 
Added it again.

## Proof of Work

Tests pass
[Test
Run](https://spruce.mongodb.com/version/6915ea856e45ed0007709db4/tasks?sorts=STATUS%3AASC%3BBASE_STATUS%3ADESC&variant=%5Eprivate_kind_code_snippets%24)

## Checklist

- [ ] Have you linked a jira ticket and/or is the ticket in the title?
- [ ] Have you checked whether your jira ticket required DOCSP changes?
- [ ] Have you added changelog file?
    - use `skip-changelog` label if not needed
- refer to [Changelog files and Release
Notes](https://github.com/mongodb/mongodb-kubernetes/blob/master/CONTRIBUTING.md#changelog-files-and-release-notes)
section in CONTRIBUTING.md for more details

Author: anandsyncs

docs/search/02-search-enterprise-deploy/code_snippets/02_0305_create_mongodb_database_resource.sh

@@ -4,7 +4,7 @@ kind: MongoDB
 metadata:
   name: ${MDB_RESOURCE_NAME}
 spec:
-  members: 3
+  members: ${MDB_MEMBERS}
   version: ${MDB_VERSION}
   type: ReplicaSet
   opsManager:

docs/search/02-search-enterprise-deploy/env_variables.sh

@@ -7,6 +7,7 @@ export MDB_NS="mongodb"
 # name of the MongoDB Custom Resource.
 export MDB_RESOURCE_NAME="mdb-rs"
 
+export MDB_MEMBERS=3
 # OM/CM's project name to be used to manage mongodb replica set
 export OPS_MANAGER_PROJECT_NAME="<arbitrary project name>"