[BUG][typescript-fetch] Output is now nested in a "src" folder which breaks typescript package references

Created by: fuzzzerd

Bug Report Checklist

Have you provided a full/minimal spec to reproduce the issue?
Have you validated the input using an OpenAPI validator (example)?
What's the version of OpenAPI Generator used?
Have you search for related issues/PRs?
What's the actual output vs expected output?

Description

Changes in this commit introduced several related bugs.

Output is now partially nested within a new src folder.
package.json.mustache was not updated to reflect this change
breaks anyone who was using local npm package references with typescript to avoid creating a separate /dist folder for the generated client code.

openapi-generator version

v4.0.3 => v4.1.0

Suggest a fix

Revert the folder name change.
Add a flag to opt in or out of the new src folder
Update the mustache templates accordingly.