Upgrade cuebot to Java 21

[DiegoTavares]

Describe the enhancement
I propose we consider upgrading cuebot from Java 8 to Java 21 alongside Spring from . This proposal is based on several key advantages that Java 21 brings to the table, including:

• New Language Features: Java 21 introduces several new language features such as local-variable type inference (var), switch expressions, text blocks, records, and pattern matching for instance of. These features can make our code more readable and efficient.

• API Improvements: There have been numerous improvements to the standard API, including the addition of the java.util.stream package in Java 8, new methods on the Optional class, the java.time package, and numerous new factory methods for collections. These improvements can help us to write more robust and maintainable code.

• Performance Improvements: Performance enhancements in Java 21, with improvements to the JVM, garbage collection, and the addition of the JMH microbenchmark suite, can lead to more efficient code execution.

• Improved Security: Java 21 has several security enhancements, including stronger algorithms and protocols, and APIs that offer more precise control over security settings. These enhancements can make our project more secure.

I have experimented upgrading in our end and aside from package compatibility issues that were all fixed by upgrading their versions, not much needed to change in the code. Besides that, all unit tests are passing and the application runs without exceptions.

Here's glimpse into the significant version changes:

• gradle 6.0.1 ->8.5
• grpc-all 1.47.0 -> 1.60.0
• protobuf-java 3.21.2 -> 3.25.1
• spring-boot-gradle-plugin 2.2.1.RELEASE -> 2.7.14
• sourceCompatibility 11 -> 21

[DiegoTavares]

@bcipriano We can discuss this in our next meeting