Fix keystore for APM-server communication

[SylvainJuge]

What does this PR do?

For the communication with APM server, we use a separate SSL context as the default that is used for the whole JVM.
That allows to implement TLS fallback and disable server certificate validation through configuration when needed.

One side effect of this was that the standard keyStore configuration parameters that are provided through JVM parameters would not be taken in account by this separate SSL context.

In short, it now means that the following parameters are now also effective for the communication with APM server, hence allowing to have client-side certificate validation.

• javax.net.ssl.keyStore
• javax.net.ssl.keyStorePassword
• javax.net.ssl.keyStoreType
• javax.net.ssl.keyStoreProvider

Checklist

• This is a bugfix
  • I have updated CHANGELOG.asciidoc
  • I have added tests that would fail without this fix
  • Manual testing with certificates provided by https://badssl.com/

[ghost]

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Build stats

• Start Time: 2021-12-21T10:46:00.591+0000

• Duration: 65 min 10 sec

• Commit: d6e3c30

Test stats 🧪

Test	Results
Failed	0
Passed	2639
Skipped	21
Total	2660

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Tests succeeded.

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[jackshirazi]

nice work!