Added strict option for RedirectPlugin

[olexiyk]

Q	A
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Related tickets	php-http/client-common#208
License	MIT

What's in this PR?

Documenting strict option for RedirectPlugin

Strict RFC compliant redirects mean that POST redirect requests are sent as POST requests vs. doing what most browsers do which is redirect POST requests with GET requests.

Example Usage

$plugins = $plugins ?? [
    new RedirectPlugin(['strict' => true]),
];

$httpClient = (new PluginClientFactory())->createClient(
    Psr18ClientDiscovery::find(),
    $plugins
);

[dbu]

thanks a lot!