Allowed markdown in footer of status page

Markdown support has been added using the marked module. To secure
against XSS attacks, DOMPurify is used to sanitize the generated HTML
before it is loaded on the page.

Signed-off-by: Matthew Nickson <mnickson@sidingsmedia.com>

package.json

@@ -81,6 +81,7 @@
         "compare-versions": "~3.6.0",
         "compression": "~1.7.4",
         "dayjs": "~1.11.5",
+        "dompurify": "^2.4.3",
         "express": "~4.17.3",
         "express-basic-auth": "~1.2.1",
         "express-static-gzip": "~2.1.7",
@@ -93,6 +94,7 @@
         "jsonwebtoken": "~9.0.0",
         "jwt-decode": "~3.1.2",
         "limiter": "~2.1.0",
+        "marked": "^4.2.5",
         "mqtt": "~4.3.7",
         "mssql": "~8.1.4",
         "mysql2": "~2.3.3",