Add issue type to issue template

[rmccar]

We can set the issue type as well as the labels etc using our GitHub issue template this will help us triage and prioritise tickets raised.

The bug template should raise a "Bug" type issue, the feature request one should raise a "Feature" type issue. To add this we just need to set type to "bug" or "feature" at the top level in the hierarchy alongside labels, title and description. The documentation for these templates is here:
https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/syntax-for-issue-forms