fix: we use sslmode not pgsslmode in the deploy repos (#957)

@marcleblanc2 pointed this out:
https://linear.app/sourcegraph/issue/REL-638/configure-aws-rds-databases-for-tls-connections-in-helm-chart

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Author: Chickensoupwithrice

docs/admin/deploy/kubernetes/index.mdx

@@ -103,7 +103,7 @@ data:
   password: ""
   port: ""
   user: ""
-  pgsslmode: "require" # optional, enable if using SSL
+  sslmode: "require" # optional, enable if using SSL
 ---
 apiVersion: v1
 kind: Secret
@@ -116,7 +116,7 @@ data:
   password: ""
   port: ""
   user: ""
-  pgsslmode: "require" # optional, enable if using SSL
+  sslmode: "require" # optional, enable if using SSL
 ---
 apiVersion: v1
 kind: Secret
@@ -129,7 +129,7 @@ data:
   password: ""
   port: ""
   user: ""
-  pgsslmode: "require" # optional, enable if using SSL
+  sslmode: "require" # optional, enable if using SSL
 ```
 
 The above Secrets should be deployed to the same namespace as the existing Sourcegraph deployment.
@@ -166,7 +166,7 @@ pgsql:
     user: "new-user"
     password: "new-password"
     port: "5432"
-    pgsslmode: "require" # optional, enable if using SSL
+    sslmode: "require" # optional, enable if using SSL
 ```
 
 #### Using external Redis instances