Add issue template, fix others

The documentation template is for a missing documentation file or
problem with documentation. This MIGHT be classified under a website
issue but it is kind of a topic on its own and as an issue for this was
recently opened (with the documentation label) this seems like a worthy
thing to have.

The bug issue template now properly adds the 'bug' label.

The other issue templates have lower case labels.

.github/ISSUE_TEMPLATE/website_issue.yml

@@ -1,7 +1,7 @@
 name: Website issue
 description: Report a problem with the website
 title: "[Website] <title>"
-labels: ["Website"]
+labels: ["website"]
 body:
 - type: checkboxes
   attributes: