Update issue templates to multiple choice

[thclark]

Also over on https://github.com/octue/octue-sdk-python

Using an ISSUE_TEMPLATE folder and markdown files within it, it's possible to give the user an improved workflow, enabling them to choose between bug reports, feature requests and support requests.

The GCR Kaniko project is an example: https://github.com/GoogleContainerTools/kaniko/tree/master/.github/ISSUE_TEMPLATE

[thclark]

Note from discussion:

• experiment with putting this in the .github repo to see if it applies to all public repos
• if it does, let's do it, otherwise apply manually to all public

[cortadocodes]

I've now implemented this globally for the Octue organisation by adding the issue templates to the .github repository. It applies to all Octue repositories (not just public ones as I thought), and includes disabling blank issues.