* Revamp issue templates

* Add “Feature request” template

* Integrate Artem’s review

- `cabal` → Cabal
- add “type: enhancement” label

* Add “Documentation” issue template

* Add labels to “Bug report” template.

“type: bug” and ”needs-triage”. Suggested by Artem.

* Add “Question” issue template

* Fix typos

Spotted by Brandon.

* Fix English in “Question” template

Fix by Brandon.

Add “needs-review” to Pull Request template

As suggested by Artem.

* Split PR template in two

Split in full (PR modifies `cabal` behaviour) and simple (otherwise).

* Add Github PR Convention to PR templates

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Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>