[improve][build] Upgrade OkHttp to 5.5.0 and Okio to 3.18.1

[lhotari]

Motivation

OkHttp and Okio are a few patch releases behind. Both are used by pulsar-broker-auth-oidc directly,
by pulsar-proxy and pulsar-broker in tests, and transitively by the Kubernetes client.

Modifications

gradle/libs.versions.toml:

library	from	to
okhttp3	5.3.2	5.5.0
okio	3.17.0	3.18.1

Plus the corresponding jar names in the server distribution LICENSE.bin.txt.

Both stay within their current major line, so the BOM-managed artifacts (okhttp-jvm,
logging-interceptor, okio-jvm) move together and no coordinate changes are needed.

Verifying this change

• Make sure that the change passes the CI checks.

This change is a trivial rework / code cleanup without any test coverage.

Verified locally with ./gradlew sanityCheck and ./gradlew checkBinaryLicense.

Does this pull request potentially affect one of the following parts:

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment