Keep low level rest client under Apache 2 software license

[mark-vieira]

Since the low level rest client (LLRC) has no dependencies on other Elasticsearch code we can continue to publish it under the Apache 2.0 license. This will also enable the future HLRC to be Apache 2.0 licensed as well, as is consistent with other client implementations.

[elasticmachine]

Pinging @elastic/es-delivery (Team:Delivery)

[jasontedor]

14:08:32 [jason@totoro:~/src/elastic/elasticsearch] llrc-apache-2+ ± ./gradlew clean :client:rest:assemble
=======================================
Elasticsearch Build Hamster says Hello!
  Gradle Version        : 6.8.2
  OS Info               : Linux 5.9.10-200.fc33.x86_64 (amd64)
  JDK Version           : 15 (Oracle)
  JAVA_HOME             : /opt/java/jdk-15
  Random Testing Seed   : 52366388B75DE731
  In FIPS 140 mode      : false
=======================================

BUILD SUCCESSFUL in 3s
326 actionable tasks: 207 executed, 2 from cache, 117 up-to-date

Publishing build scan...
https://gradle-enterprise.elastic.co/s/esxgqobdnbhk4

14:08:47 [jason@totoro:~/src/elastic/elasticsearch] llrc-apache-2+ ± xmlstarlet sel -N pom="http://maven.apache.org/POM/4.0.0" -t -c '/pom:project/pom:licenses' -nl client/rest/build/distributions/elasticsearch-rest-client-8.0.0-SNAPSHOT.pom
<licenses xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
    <license>
      <name>The Apache Software License, Version 2.0</name>
      <url>http://www.apache.org/licenses/LICENSE-2.0</url>
      <distribution>repo</distribution>
    </license>
  </licenses>
14:08:59 [jason@totoro:~/src/elastic/elasticsearch] llrc-apache-2+ ± 

LGTM