[sitecore-jss-proxy] Setting "followRedirects" to true" breaks HEAD requests

[illiakovalenko]

• This PR follows the Contribution Guide
• Changelog updated

Description / Motivation

When customers use followRedirects: true and try to send a HEAD request, the proxy server crashes.
This PR addresses this problem. When followRedirects is enabled, http-proxy-middleware initializes a proxy request before onProxyReq is called, after it's initialized there is no way to update the method without accessing to internal properties, so we swap HEAD with GET before onProxyReq is called, and change it back in onProxyReq event in case it's accessed later.

This change shouldn't be treated as a breaking change, since Express middleware accepts an array of handlers also.

Testing Details

• Unit Test Added
• Manual Test/Other (Please elaborate)

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)