Improve type-safety: use autogenerated types across frontend codebase (part 1)

[brojd]

Part 1 of using autogenerated types, we should cover here alert groups, integrations and users

Acceptance criteria

• frontend has additional layer for making HTTP requests
• every HTTP request goes through this layer (e.g. prevent calling makeRequest directly from components or MobX stores)
• in this layer every HTTP request and response is typed using types imported from files generated as a part of https://github.com/grafana/oncall/issues/3330
• any other frontend code make use of generated types instead of custom types (e.g. use enum from generated types instead of manual string etc.)

Outcome

• better type-safety in code
• being able to catch type errors during development before they reach prod (shift left)
• better developer experience thanks to increased number of type declarations and improved intellisense