[Improvement] Introduce Maven Modernizer plugin to Pulsar

[MarvinCai]

As discussed in dev mail list: https://lists.apache.org/thread.html/re99b342765b2cfb26f3da0eedfb78e7312de158bf6c7ed0085d32781%40%3Cdev.pulsar.apache.org%3E
We want to introduce Maven Modernizer plugin to Pulsar.
This plugin helps detecting uses of legacy APIs which can be replaced with modern APIs that are often more performant, safer, and idiomatic than the legacy equivalents.
We'll break down the task by sub-module so anyone interested can work on a sub-module independently.
We'll start with checking violation with Java 8. Acceptance criteria will be passing existing CI.
Help are welcome, please reply with module you want to work on so there won't be conflict. And if change for single module is too big, please break down pr to reasonable size, say < 100 change so it's easier to review.
Please don't close the master issue via comment.

<plugin>
    <groupId>org.gaul</groupId>
    <artifactId>modernizer-maven-plugin</artifactId>
    <configuration>
        <failOnViolations>true</failOnViolations>
        <javaVersion>8</javaVersion>
    </configuration>
    <executions>
        <execution>
            <id>modernizer</id>
            <goals>
                <goal>modernizer</goal>
            </goals>
        </execution>
    </executions>
</plugin>

• managed-ledger
• pulsar-common
• pulsar-broker-common
• pulsar-broker-auth-athenz
• pulsar-broker-auth-sasl
• pulsar-broker
• pulsar-client-api
• pulsar-client
• pulsar-client-admin-api
• pulsar-client-admin
• pulsar-client-tools
• pulsar-client-tools-test
• pulsar-client-auth-athenz
• pulsar-client-auth-sasl
• pulsar-websocket
• pulsar-proxy
• pulsar-discovery-service
• pulsar-zookeeper-utils
• pulsar-testclient
• pulsar-config-validation
• pulsar-transaction
• pulsar-functions
• pulsar-metadata
• pulsar-package-management

[MarvinCai]

Please tag with help-wanted & good-first-issue
I'll work on pulsar-common

[amarlearning]

@MarvinCai @eolivelli I would like to work on pulsar-proxy 😄

[github-actions]

The issue had no activity for 30 days, mark with Stale label.

[youzipi]

i will work on pulsar-transaction and pulsar-broker @MarvinCai

[tisonkun]

@MarvinCai you can create a subtask for pulsar-broker for @youzipi, ask them to comment there, and assign.

Although, pulsar-broker is a heated code path various patches modify its code. @youzipi you may find a way to separate it into more fine-grained patches to avoid conflict or contact with domain experts like @codelipenghui to cooperate on that module. I assume that applying this plugin is like a code style reformat among the whole module.

[MarvinCai]

@tisonkun seems we've enabled the plugin for all modules, can close this issue?

[tisonkun]

@MarvinCai No. There're still several dangling issues:

• [cleanup][broker][Modernizer] fix violations in pulsar-broker #17275
• [Modernizer] Apply modernizer plugin to pulsar-broker modules. #16991

[tisonkun]

Concretely, we turn on the plugin for pulsar-broker, but ignore several patterns now for gradually handling them. I think @youzipi is actively working on this. We can help with reviewing.

Flaky tests hurt a lot :(

[tisonkun]

@MarvinCai @codelipenghui @nodece should be closed by #17968.