Loading ConnectionMetaData from the agent class loader

[eyalkoren]

What does this PR do?

The theory:
When multiple JDBC implementations on a Servlet container share a data source, they may also share JDBC connection instances. Since the connection --> metadata cache is managed as a global state across the entire JVM, and the created ConnectionMetaData values stored in it are created by the plugin, this may cause a ClassCastException if one JDBC driver is storing a metadata instance for a connection instance and another one is retrieving it.
Normally this is not an issue because there will be a single JDBC dependency, but there may be cases where there are multiple JDBC dependencies. It still requires a special setup where java.sql.Statement implementations are loaded from some class loader while the java.sql.Connection class is shared, so that the connection instances can be shared.

This PR fixes the issue by ensuring that the ConnectionMetaData is always loaded only by the agent class loader.

Checklist

• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix

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• Build Cause: Branch indexing

• Start Time: 2021-06-23T16:39:18.246+0000

• Duration: 57 min 6 sec

• Commit: 430b8d7

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Failed	0
Passed	2245
Skipped	18
Total	2263

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Passed	2245
Skipped	18
Total	2263

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• Build Cause: Pull request #1864 updated

• Start Time: 2021-06-24T07:53:25.894+0000

• Duration: 56 min 42 sec

• Commit: 6467d4f

Test stats 🧪

Test	Results
Failed	0
Passed	2286
Skipped	19
Total	2305

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Test stats 🧪

Test	Results
Failed	0
Passed	2286
Skipped	19
Total	2305