Add issue and merge request templates for the Web Admin project in Gitlab

Problem/Motivation

Add description templates to help your contributors to communicate effectively!

Proposed resolution

• Create an issue template
• Create a merge request template
• Use the templates
• Set a default template for merge requests and issues (PREMIUM)

Checkpoints

• ☑ File an issue
• ☑ Addition/Change/Update/Fix
• ☑ Testing to ensure no regression
• ☐ Automated unit testing coverage
• ☐ Automated functional testing coverage
• ☐ UX/UI designer responsibilities
• ☑ Readability
• ☑ Accessibility
• ☑ Performance
• ☑ Security
• ☑ Documentation
• ☑ Code review by maintainers
• ☑ Full testing and approval
• ☑ Credit contributors
• ☑ Review with the product owner
• ☐ Release Notes
• ☐ Release webadmin-9.0.2

User interface changes

API changes

Data model changes