Provide self-descriptive text for selectdb/doris.fe-ubuntu and selectdb/doris.be-ubuntu on Docker Hub

[linghengqian]

• I noticed from Improve GraalVM Reachability Metadata and corresponding nativeTest related unit tests shardingsphere#29052 that the direct way to bypass compiling Doris Docker Image is to use https://github.com/apache/doris-operator on kubernetes.
• But using kubernetes operator in unit tests is very taxing on the 4C/16gb Github Runner device. If I want to write integration tests for doris, I need to first start a k3s cluster with docker via testcontainers-java, and then deploy doris's kubernetes operator on the k3s cluster, which almost certainly causes out of memory issues on the Github Runner device because shardingsphere also resident additional hotspot vm processes or graalvm native image processes on the Github Runner device.
• I noticed that https://github.com/apache/doris-operator/blob/release-24.0.0/helm-charts/doris/values.yaml is using selectdb/doris.fe-ubuntu and selectdb/doris.be-ubuntu. But neither of these two Docker Images has self-descriptive text.
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• It would be nice if these two Docker Images have self-descriptive text to describe how to use them. This would avoid dynamically downloading binaries and generating Docker Images in the context of testcontainers-java, and also avoid starting a k3s cluster.