osquerybeat/ext: Make packages non-internal.

[yashtewari]

What does this PR do?

Changes the following packages to be non-internal

• github.com/elastic/beats/v7/x-pack/osquerybeat/ext/osquery-extension/internal/hostfs
• github.com/elastic/beats/v7/x-pack/osquerybeat/ext/osquery-extension/internal/proc
• github.com/elastic/beats/v7/x-pack/osquerybeat/ext/osquery-extension/internal/tables

Why is it important?

These packages can now be used from outside osquerybeat

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.

[mergify]

This pull request does not have a backport label. Could you fix it @yashtewari? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit

NOTE: backport-skip has been added to this pull request.

[aleksmaus]

LGTM 👍

[elasticmachine]

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• Start Time: 2022-01-25T14:40:59.241+0000

• Duration: 64 min 7 sec

• Commit: 9d0dab2

Test stats 🧪

Test	Results
Failed	0
Passed	4083
Skipped	0
Total	4083

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