Fix APM Server version parsing

[eyalkoren]

What does this PR do?

Adjusting APM Server version parsing to match 7.16+

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have updated CHANGELOG.asciidoc
  • I have added tests that prove my fix is effective or that my feature works
  • Tested manually with
    • 6.8.20
    • 7.0.0
    • 7.11.2
    • 7.16.0
    • 8.0.0-beta1

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Build stats

• Start Time: 2021-12-06T14:05:13.027+0000

• Duration: 69 min 9 sec

• Commit: b1c9da7

Test stats 🧪

Test	Results
Failed	0
Passed	2627
Skipped	21
Total	2648

💚 Flaky test report

Tests succeeded.

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