[fix][build] Remove jetty-server from avroTools Gradle configuration used in build

[lhotari]

Motivation

There are GitHub Dependabot security alerts about Jetty 9. The source of them is this build logic:

pulsar/pulsar-client/build.gradle.kts

Lines 90 to 104 in a1613bc

	// Generate Avro test classes from .avsc schema files
	val avroTools by configurations.creating
	dependencies {
	avroTools("org.apache.avro:avro-tools:${libs.versions.avro.get()}")
	}
	val generateTestAvro by tasks.registering(JavaExec::class) {
	val avscDir = file("src/test/resources/avro")
	val outputDir = layout.buildDirectory.dir("generated-sources/avro-test")
	inputs.dir(avscDir)
	outputs.dir(outputDir)
	classpath = avroTools
	mainClass.set("org.apache.avro.tool.Main")
	args("compile", "schema", avscDir.absolutePath, outputDir.get().asFile.absolutePath)
	}

This is used in pulsar-client's build to generate avro classes from the schema for tests.

The dependency enforcement solution in the Pulsar Gradle build doesn't apply to all Gradle configurations. It's only applied to implementation (and configurations extending implementation). avroTools is an independent configuration.

Modifications

Exclude jetty-server dependency since it's not needed at all.