docs: add steps for postgres server verification (#12072)

* docs: add steps for postgres server verification

* make: fmt

* refactor to guide

* add manifest

docs/guides/postgres-ssl.md

@@ -0,0 +1,77 @@
+# Configure Coder to connect to PostgreSQL using SSL
+
+<div>
+  <a href="https://github.com/ericpaulsen" style="text-decoration: none; color: inherit;">
+    <span style="vertical-align:middle;">Eric Paulsen</span>
+    <img src="https://github.com/ericpaulsen.png" width="24px" height="24px" style="vertical-align:middle; margin: 0px;"/>
+  </a>
+</div>
+February 24, 2024
+
+---
+
+Your organization may require connecting to the database instance over SSL. To
+supply Coder with the appropriate certificates, and have it connect over SSL,
+follow the steps below:
+
+## Client verification (server verifies the client)
+
+1. Create the certificate as a secret in your Kubernetes cluster, if not already
+   present:
+
+```shell
+kubectl create secret tls postgres-certs -n coder --key="postgres.key" --cert="postgres.crt"
+```
+
+1. Define the secret volume and volumeMounts in the Helm chart:
+
+```yaml
+coder:
+  volumes:
+    - name: "pg-certs-mount"
+      secret:
+        secretName: "postgres-certs"
+  volumeMounts:
+    - name: "pg-certs-mount"
+      mountPath: "$HOME/.postgresql"
+      readOnly: true
+```
+
+1. Lastly, your PG connection URL will look like:
+
+```shell
+postgres://<user>:<password>@databasehost:<port>/<db-name>?sslmode=require&sslcert="$HOME/.postgresql/postgres.crt&sslkey=$HOME/.postgresql/postgres.key"
+```
+
+## Server verification (client verifies the server)
+
+1. Download the CA certificate chain for your database instance, and create it
+   as a secret in your Kubernetes cluster, if not already present:
+
+```shell
+kubectl create secret tls postgres-certs -n coder --key="postgres-root.key" --cert="postgres-root.crt"
+```
+
+1. Define the secret volume and volumeMounts in the Helm chart:
+
+```yaml
+coder:
+  volumes:
+    - name: "pg-certs-mount"
+      secret:
+        secretName: "postgres-certs"
+  volumeMounts:
+    - name: "pg-certs-mount"
+      mountPath: "$HOME/.postgresql/postgres-root.crt"
+      readOnly: true
+```
+
+1. Lastly, your PG connection URL will look like:
+
+```shell
+postgres://<user>:<password>@databasehost:<port>/<db-name>?sslmode=verify-full&sslrootcert="/home/coder/.postgresql/postgres-root.crt"
+```
+
+> More information on connecting to PostgreSQL databases using certificates can
+> be found
+> [here](https://www.postgresql.org/docs/current/libpq-ssl.html#LIBPQ-SSL-CLIENTCERT).