Fix server-side divergences between form-v2/develop and develop branch

[karrui]

This issue keeps track of the various server-side divergences between the form-v2/develop and develop branch, so we hopefully only need to migrate infra + react related code instead of also having to check for server-side variances.

• shared/constants/form.ts
  

• shared/types/core.ts
  

• shared/types/form/form.ts
  

• shared/types/user.ts
  

• shared/utils/file-validation.ts
  export const VALID_EXTENSIONS

• shared/utils/immutable-array-fns.ts

  • Not used in server, can keep it in react branch for now
    Add

export const insertAt = <T>(
  array: ExtractTypeFromArray<T>[],
  index: number,
  valueToInsert: ExtractTypeFromArray<T>,
): ExtractTypeFromArray<T>[] => {
  return [...array.slice(0, index), valueToInsert, ...array.slice(index)]
}

• Add positional API (documented in feat(builder/4): add form field creation feature in form builder, extend create field API with positional arg #3135

  • src/app/models/form.server.model.ts
  • src/app/modules/form/admin-form/admin-form.controller.ts
  • src/app/modules/form/admin-form/admin-form.service.ts
  • src/types/form.ts

• Add env var route (documented in feat(form-v2): add /client/env route for sending client env vars as JSON #2878)

  • src/app/modules/frontend/frontend.controller.ts
  • src/app/modules/frontend/frontend.routes.ts
  • src/app/modules/frontend/frontend.service.ts
  • src/app/routes/api/v3/client/client.routes.ts

/**
 * Handler for GET /frontend/env endpoint.
 * @returns the environment variables needed to hydrate the frontend.
 */
export const handleGetEnvironment: ControllerHandler<never, ClientEnvVars> = (
  _req,
  res,
) => {
  return res.json(getClientEnvVars())
}

• src/app/modules/user/user.controller.ts
  Update types
  

• src/app/modules/user/user.utils.ts
  Remove InvalidOtpError -> unauthorised (will remove login session)
  

• src/types/api/form_auth.ts
  Not used in react, so not updating for now

[karrui]

Closed by above PRs.