chore: add discussion templates for general category

[mitsudome-r]

Description

This adds template for General category in GitHub Discussion. We are having some bots spamming our Discussion board, and I'm hoping this could mitigate those spams.

Tests performed

You can try creating Discussion on my fork to check how it looks.

Notes for reviewers

None

Interface changes

None

Effects on system behavior

People would have to fill in a template when they create a Discussion under General category

Pre-review checklist for the PR author

The PR author must check the checkboxes below when creating the PR.

• [x] I've confirmed the contribution guidelines.
• [x] The PR follows the pull request guidelines.

In-review checklist for the PR reviewers

The PR reviewers must check the checkboxes below before approval.

• [x] The PR follows the pull request guidelines.
• [x] The PR has been properly tested.
• [x] The PR has been reviewed by the code owners.

Post-review checklist for the PR author

The PR author must check the checkboxes below before merging.

• [ ] There are no open discussions or they are tracked via tickets.
• [ ] The PR is ready for merge.

After all checkboxes are checked, anyone who has write access can merge the PR.

[xmfcx]

Adding this here for reference:

• https://docs.github.com/en/discussions/managing-discussions-for-your-community/syntax-for-discussion-category-forms