feat: support String-Array query parameter in DP public API

[paullatzelsperger]

What this PR changes/adds

This PR adds support for multiple identical HTTP query parameters. For example, parameters like foo=bar&foo=baz were collapsed, and only foo=bar was forwarded to the HTTP target.
With this PR, the same query param string is preserved as string-array.

Why it does that

A Tractus-X system standard requires the support of string-array query parameters.

Further notes

• the DataPlanePublicApiEndToEndTest was improved to verify HTTP requests using the Netty MockServer (instead of calling a dummy URL)
• The DataPlanePublicApiV2 now supports HEAD requests, they were missing before.
• By default, requests that hit the public API of the dataplane are classified as PULL flows

NB: that this behaviour will NOT be backported to the legacy version of the public dataplane API!

Linked Issue(s)

Closes #4022

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