fix(opengraph): treat user frontmatter values as String

A bug was reported that having frontmatter fields being only numeric results in an error. This seems to be caused
as the frontmatter is processed by the yaml-parser but returned
with the types as given. So a numeric value is returned as a number,
a "true" or "false" is returned as boolean etc.
As we expect strings in the template, that resulted in an exception.

This commit fixes this by treating every value as string in the template.
Since we've got no other usages of opengraph data, this should not have been
a security problem.

Signed-off-by: Erik Michelson <github@erik.michelson.eu>

public/docs/release-notes.md

@@ -5,6 +5,9 @@
 ### Enhancements
 - Add a pointer to Mermaid 9.1.7 documentation, which is what HedgeDoc 1 supports.
 
+### Bugfixes
+- Fix a crash when having numeric-only values in opengraph frontmatter
+
 ## <i class="fa fa-tag"></i> 1.9.9 <i class="fa fa-calendar-o"></i> 2023-07-30
 
 HedgeDoc has a new slogan! See [our announcement](https://community.hedgedoc.org/t/and-the-new-slogan-is/) for the details.

public/views/hedgedoc/head.ejs

@@ -6,8 +6,8 @@
 <meta name="mobile-web-app-capable" content="yes">
 <%- include('../includes/favicon') %>
 <% for (var og in opengraph) { %>
-<% if (opengraph.hasOwnProperty(og) && opengraph[og].trim() !== '') { %>
-<meta property="og:<%= og %>" content="<%= opengraph[og] %>">
+<% if (opengraph.hasOwnProperty(og) && String(opengraph[og]).trim() !== '') { %>
+<meta property="og:<%= og %>" content="<%= String(opengraph[og]) %>">
 <% }} if (!opengraph.hasOwnProperty('image')) { %>
 <meta property="og:image" content="<%- serverURL %>/icons/android-chrome-512x512.png">
 <meta property="og:image:alt" content="HedgeDoc logo">