Add backwards compatibility with Golang 1.13.x to support Google Cloud Functions

[kvch]

What does this PR do?

This PR adds backwards compatibility with Golang 1.13.x. The unsupported features were VerifyConnections introduced in #22495 and TLSDialContext from #25219

Why is it important?

Google Cloud Function run in Golang 1.13.8 environment. Previously, Beats only supported the version in the file .go-version. To make sure users can deploy and run Functionbeat on GCP these changes are required.

Also, we need to include some backwards compatibility smoke test or whatever so we are not breaking GCP functions in the future.

Checklist

• My code follows the style guidelines of this project
  - [ ] I have commented my code, particularly in hard-to-understand areas
  - [ ] I have made corresponding changes to the documentation
  - [ ] I have made corresponding change to the default configuration files
  - [ ] I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

Closes #24925

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[urso]

Is there a chance we can reduce the amount of copy and paste code?

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2021-07-22T13:09:09.197+0000

• Duration: 142 min 2 sec

• Commit: f81e97c

Test stats 🧪

Test	Results
Failed	0
Passed	49440
Skipped	5396
Total	54836

Trends 🧪

💚 Flaky test report

Tests succeeded.

Expand to view the summary

Test stats 🧪

Test	Results
Failed	0
Passed	49440
Skipped	5396
Total	54836

[urso]

That change hurts. I still see why it is supported for GCP support :(

[botelastic]

Hi!
We just realized that we haven't looked into this PR in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it in as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b fix-functionbeat-gcp-tls upstream/fix-functionbeat-gcp-tls
git merge upstream/master
git push upstream fix-functionbeat-gcp-tls

[kvch]

New temp fix: #28251