Unable to use "+" character in query parameters

## The feature or bug you are proposing

The `+` character is removed when parameters are parsed if the params are not URL encoded. E.g. using an "email" parameter with `gbarbon+2@anemailprovider.org` value (in a GET) returns an empty array, instead of returning the array with the corresponding user.

## The description of the bug or the rationale of your proposal
More precisely, the `+` character is substituted by fastify when parsing the query params, since the `+` char in a query parameters correspond to the whitespace character (see [here](https://stackoverflow.com/questions/6855624/plus-sign-in-query-string#:~:text=%2B%20sign%20has%20a%20semantic%20meaning,pairs%20in%20the%20query%20string) for further info).

## The expected result for your bug
The plugin should encode the URL, in such a way to avoid loosing special characters when they reach fastify.

However, we're not 100% sure that the plugin should perform the encoding automatically. Please also note that this feature might be breaking if someone is inserting the `+` char in the query parameter in order to insert a whitespace on purpose.

Start by tracing how the plugin builds GET requests and how Fastify parses their query parameters. Reproduce the email value containing `+`, then determine the intended handling for literal plus signs versus spaces; done should include verified behavior for both cases.

Written by the indexing model from the issue text.