fix(storage): preserve port in spring.cloud.gcp.storage.host (#4343)

[kioie]

Description

Fixes #4343

Problem:
When configuring spring.cloud.gcp.storage.host with a custom port (such as for a local emulator or fake-gcs-server Testcontainers setup), the port number was being silently removed by GcpStorageAutoConfiguration. Specifically, verifyAndFetchHost() used URL.getHost() which only returns the hostname portion. This resulted in http://localhost:54321 being incorrectly transformed to http://localhost/, causing Connection refused errors during integration tests.

Solution:
Replaced url.getHost() with url.getAuthority() in GcpStorageAutoConfiguration.java. url.getAuthority() properly returns host:port when a port is present, and behaves identically to url.getHost() when no port is configured, guaranteeing no breaking regressions for existing configurations.

Contribution Checklist

• Issue Linked: This PR addresses an existing issue (Bug Report: spring.cloud.gcp.storage.host Drops Port Number #4343) that has been labeled with "Accepting Contributions".
• Clear Description: The PR description clearly states the problem and the proposed solution.
• Unit Tests: Added a new unit test (testHostWithPort()) in GcpStorageAutoConfigurationTests.java to explicitly test and prevent regressions of hosts configured with ports.
• Tests Passed: Verified that all existing and new unit tests pass successfully (./mvnw -pl spring-cloud-gcp-autoconfigure test -Dtest=GcpStorageAutoConfigurationTests).
• Code Formatting: Ensured the code conforms to the Google Java Style Guide (verified via the validate-google-style checkstyle plugin check running without errors).
• CLA Signed: (I have signed the Contributor License Agreement).