fix duplicated classes in bootstrap jar

[SylvainJuge]

What does this PR do?

Fixes a packaging issue introduced with #2341.
Classes that are copied as resources are being added to the bootstrap jar, and as a result Jacoco fails due to duplicated bytecode. In practice it might not have any effect at runtime as the classes are loaded by location only and can't be accessed by standard classloaders.

Doing a simple unzip -l apm-agent-bootstrap/target/apm-agent-bootstrap-1.28.2-SNAPSHOT.jar shows the issue.

Before:

Archive:  apm-agent-bootstrap/target/apm-agent-bootstrap-1.28.2-SNAPSHOT.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2021-12-16 09:53   META-INF/
       81  2021-12-16 09:53   META-INF/MANIFEST.MF
        0  2021-12-16 09:53   java/
        0  2021-12-16 09:53   java/lang/
     2899  2021-12-16 09:53   java/lang/IndyBootstrapDispatcher.class
        0  2021-12-16 09:53   bootstrap/
        0  2021-12-16 09:53   bootstrap/java/
        0  2021-12-16 09:53   bootstrap/java/lang/
     2899  2021-12-16 09:53   bootstrap/java/lang/IndyBootstrapDispatcher.esclazz
        0  2021-12-16 09:53   co/
        0  2021-12-16 09:53   co/elastic/
        0  2021-12-16 09:53   co/elastic/apm/
        0  2021-12-16 09:53   co/elastic/apm/agent/
        0  2021-12-16 09:53   co/elastic/apm/agent/modulesetter/
     1912  2021-12-16 09:53   co/elastic/apm/agent/modulesetter/ModuleSetter.class
        0  2021-12-16 09:53   bootstrap/co/
        0  2021-12-16 09:53   bootstrap/co/elastic/
        0  2021-12-16 09:53   bootstrap/co/elastic/apm/
        0  2021-12-16 09:53   bootstrap/co/elastic/apm/agent/
        0  2021-12-16 09:53   bootstrap/co/elastic/apm/agent/modulesetter/
     1912  2021-12-16 09:53   bootstrap/co/elastic/apm/agent/modulesetter/ModuleSetter.esclazz
        0  2021-12-16 09:53   META-INF/maven/
        0  2021-12-16 09:53   META-INF/maven/co.elastic.apm/
        0  2021-12-16 09:53   META-INF/maven/co.elastic.apm/apm-agent-bootstrap/
     6624  2021-12-16 09:53   META-INF/maven/co.elastic.apm/apm-agent-bootstrap/pom.xml
       78  2021-12-16 09:53   META-INF/maven/co.elastic.apm/apm-agent-bootstrap/pom.properties
---------                     -------
    16405                     26 files

After the change:

Archive:  apm-agent-bootstrap/target/apm-agent-bootstrap-1.28.2-SNAPSHOT.jar
  Length      Date    Time    Name
---------  ---------- -----   ----
        0  2021-12-16 09:45   bootstrap/
        0  2021-12-16 09:45   bootstrap/co/
        0  2021-12-16 09:45   bootstrap/co/elastic/
        0  2021-12-16 09:45   bootstrap/co/elastic/apm/
        0  2021-12-16 09:45   bootstrap/co/elastic/apm/agent/
        0  2021-12-16 09:45   bootstrap/co/elastic/apm/agent/modulesetter/
        0  2021-12-16 09:45   bootstrap/java/
        0  2021-12-16 09:45   bootstrap/java/lang/
     1912  2021-12-16 09:45   bootstrap/co/elastic/apm/agent/modulesetter/ModuleSetter.esclazz
     2899  2021-12-16 09:45   bootstrap/java/lang/IndyBootstrapDispatcher.esclazz
---------                     -------

[apmmachine]

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• Start Time: 2021-12-16T09:27:09.012+0000

• Duration: 70 min 41 sec

• Commit: 0d3a35f

Test stats 🧪

Test	Results
Failed	0
Passed	2639
Skipped	21
Total	2660

💚 Flaky test report

Tests succeeded.

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