Compile only opentelemetry-api dependency

[jack-berg]

Resolves #25.

When I ./gradlew publishToMavenLocal I get the following in my pom file:

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <!-- This module was also published with a richer model, Gradle metadata,  -->
  <!-- which should be used instead. Do not delete the following line which  -->
  <!-- is to indicate to Gradle or any Gradle module metadata file consumer  -->
  <!-- that they should prefer consuming it instead. -->
  <!-- do_not_remove: published-with-gradle-metadata -->
  <modelVersion>4.0.0</modelVersion>
  <groupId>io.opentelemetry.semconv</groupId>
  <artifactId>opentelemetry-semconv</artifactId>
  <version>1.21.0-alpha-SNAPSHOT</version>
  <name>OpenTelemetry Semantic Conventions Java</name>
  <description>OpenTelemetry Semantic Conventions generated classes for Java</description>
  <url>https://github.com/open-telemetry/semantic-conventions-java</url>
  <licenses>
    <license>
      <name>The Apache License, Version 2.0</name>
      <url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
    </license>
  </licenses>
  <developers>
    <developer>
      <id>opentelemetry</id>
      <name>OpenTelemetry</name>
      <url>https://github.com/open-telemetry/community</url>
    </developer>
  </developers>
  <scm>
    <connection>scm:git:git@github.com:open-telemetry/semantic-conventions-java.git</connection>
    <developerConnection>scm:git:git@github.com:open-telemetry/semantic-conventions-java.git</developerConnection>
    <url>git@github.com:open-telemetry/semantic-conventions-java.git</url>
  </scm>
</project>

[gaeljw]

Thanks!