feat: add docs for tls_client_ca_certificate (#72)

Author: lars-berger

docs/configuration/pgdog.toml/general.md

@@ -86,6 +86,12 @@ Reject clients that connect without TLS. Consider setting this to `true` when us
 
 Default: **`false`** (disabled)
 
+### `tls_client_ca_certificate`
+
+Path to a certificate bundle used for mTLS client certificate validation on TLS connection creation. If provided, clients without a valid certificate are rejected at the handshake. Set [`tls_client_required`](#tls_client_required) to additionally require TLS itself.
+
+Default: **none**
+
 ### `tls_verify`
 
 How to handle TLS connections to Postgres servers. By default, PgDog will attempt to establish TLS and will accept _any_ server certificate.

docs/migrating-to-pgdog/from-pgbouncer.md

@@ -225,7 +225,7 @@ Settings that control how client and server connections use TLS.
 | [`client_tls_sslmode`](https://www.pgbouncer.org/config.html#client_tls_sslmode) | [`tls_client_required`](../configuration/pgdog.toml/general.md#tls_client_required) | Boolean setting in PgDog only. `true` forces clients to use TLS, `false` doesn't. |
 | [`client_tls_key_file`](https://www.pgbouncer.org/config.html#client_tls_key_file) | [`tls_private_key`](../configuration/pgdog.toml/general.md#tls_private_key) | - |
 | [`client_tls_cert_file`](https://www.pgbouncer.org/config.html#client_tls_cert_file) | [`tls_certificate`](../configuration/pgdog.toml/general.md#tls_certificate) | - |
-| [`client_tls_ca_file`](https://www.pgbouncer.org/config.html#client_tls_ca_file) | N/A | mTLS is not currently supported in PgDog. |
+| [`client_tls_ca_file`](https://www.pgbouncer.org/config.html#client_tls_ca_file) | [`tls_client_ca_certificate`](../configuration/pgdog.toml/general.md#tls_client_ca_certificate) | Enables mTLS for client connections. |
 | [`client_tls_protocols`](https://www.pgbouncer.org/config.html#client_tls_protocols) | N/A | Only modern and secure protocols are supported. |
 | [`client_tls_ciphers`](https://www.pgbouncer.org/config.html#client_tls_ciphers) | N/A | Same as above. |
 | [`client_tls13_ciphers`](https://www.pgbouncer.org/config.html#client_tls13_ciphers) | N/A | Same as above. |