Pin JAEGER_VERSION default to 2.13.0 in integration tests

[Copilot]

❗ This PR cannot be merged until next release of Jaeger where Cassandra schema container is released as v2.

The CI e2e integration tests used :latest tag for Jaeger containers, causing unpredictable test behavior across versions.

Changes

• Changed jaegerVersion() default from "latest" to "2.13.0" in DependenciesTest.java
• Updated README to document the new default

The JAEGER_VERSION environment variable and jaeger.version system property remain available for overrides.

public static String jaegerVersion() {
  String jaegerVersion = System.getProperty("jaeger.version", System.getenv("JAEGER_VERSION"));
  return jaegerVersion != null ? jaegerVersion : "2.13.0";  // was "latest"
}

Original prompt

the ci.yaml workflow runs e2e integration tests that are starting unified jaeger container with the tag :latest. I want to change it to have a mandatory environment variable JAEGER_VERSION which should default to 2.13.0

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