Add audit logging for all mutating gRPC operations

Log Info-level audit events on success for:
- system: Init, Unseal, Seal
- auth: Login, Logout
- engine: Mount, Unmount
- policy: CreatePolicy, DeletePolicy
- ca: ImportRoot, CreateIssuer, DeleteIssuer, IssueCert, RenewCert

Each log line includes relevant identifiers (mount, issuer, serial, CN,
SANs, username) so that certificate issuance and other privileged
operations are traceable in the server logs.

Co-authored-by: Junie <junie@jetbrains.com>

web/templates/issuer_detail.html

@@ -45,12 +45,12 @@
             <tbody>
             {{range .Certs}}
             <tr>
-                <td>{{index . "cn"}}</td>
-                <td>{{index . "profile"}}</td>
-                <td><code>{{index . "serial"}}</code></td>
-                <td>{{index . "issued_by"}}</td>
-                <td>{{index . "issued_at"}}</td>
-                <td>{{index . "expires_at"}}</td>
+                <td>{{.CommonName}}</td>
+                <td>{{.Profile}}</td>
+                <td><code>{{.Serial}}</code></td>
+                <td>{{.IssuedBy}}</td>
+                <td>{{.IssuedAt}}</td>
+                <td>{{.ExpiresAt}}</td>
             </tr>
             {{end}}
             </tbody>