Merge request default template and updated CONTRIBUTING.md

Description and notes

Updated CONTRIBUTING.md and added .gitlab/merge_request_templates/default.md

Merge Checklist

• I have read CONTRIBUTING.md
  • and
    • my code editor has
      • ESLint support enabled
      • TypeScript support enabled
      • some form of spell checker
        • We suggest using a spell checker compatible with cSpell if possible
    • my changes compile successfully and seem to work properly
    • I am using the simple compiler (simple-compiler.[bat or sh])
    • I am using the normal compiler (compile.[bat or sh])
    • this is my first merge request
    • the changes in this merge request comply with the coding style defined in CONTRIBUTING.md

Changes made

• Fixed some wording in .gitlab/issue_templates/bug_report.md
• Added .gitlab/merge_request_templates/default.md which GitGud should automatically use as the default template for new merge requests
  • I have manually applied the template to this merge request so that you can get a feel for how it will look
• Fixes some wording in CONTRIBUTING.md and adds more info to it

Things left to do

• code review (this is done by one or more people other than you)
• let Pregmodder know that this is ready for merging