Add configuration for custom base URL and auth headers for Java

[daniel-mohedano]

What does this PR do?

• Adds the following variables for the Java tracer installation:
  • DD_SET_TRACER_REPOSITORY_URL_JAVA: (optional) Base URL of a Maven repository (or proxy/mirror) used to download the Java tracer JAR and its .sha256. The path under the base must follow the standard Maven layout for com.datadoghq:dd-java-agent (i.e. <base>/<version>/dd-java-agent-<version>.jar, plus <base>/maven-metadata.xml when DD_SET_TRACER_VERSION_JAVA is not pinned). Trailing slashes are tolerated. Defaults to https://repo1.maven.org/maven2/com/datadoghq/dd-java-agent.
  • DD_SET_AUTH_HEADER_JAVA: (optional) HTTP header used to authenticate against DD_SET_TRACER_REPOSITORY_URL_JAVA, provided as a complete Name: Value string (e.g. Authorization: Bearer <token>). Passed verbatim to curl -H / wget --header on every Java tracer download. Requires DD_SET_TRACER_REPOSITORY_URL_JAVA to be set to a custom repository URL. Redirects are not followed when this option is set, to avoid forwarding credentials to another location; configure DD_SET_TRACER_REPOSITORY_URL_JAVA as the final repository URL.

These two changes allow customers to download the tracer from a local repository or custom proxy/mirror to avoid hitting rate limits from Maven central. When not set, the behavior defaults to the old one.

Motivation

Additional Notes

Possible Drawbacks / Trade-offs

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