Set OIDC proxy state cookie during the local redirect

[sberyozkin]

Fixes #93.

Please see the linked issue description.
OIDC proxy code update is only about setting a state cookie and verifying it is correct at the end of the local redirect.
Reworking the test proved more difficult, but was worth, as the local redirect, even though it was already used in the test, was not really deeply verified.

[Copilot]

Pull Request Overview

This PR addresses issue #93 by introducing a mechanism to set and verify a dedicated OIDC proxy state cookie during the local redirect process.

• Introduces a new constant and functions to create and remove the OIDC proxy state cookie in OidcProxy.java
• Updates the local redirect flow to validate the state cookie and enhances error handling when state validation fails
• Modifies integration tests to validate the new cookie behavior and updates application properties accordingly

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
runtime/src/main/java/io/quarkus/oidc/proxy/runtime/OidcProxy.java	Added cookie creation and verification logic for the proxy state to secure the local redirect flow
integration-tests/src/test/java/io/quarkus/oidc/proxy/OidcProxyTestCase.java	Updated tests to check for the correct handling of the proxy state cookie during redirects
integration-tests/src/main/resources/application.properties	Added configuration to disallow multiple code flows