Cherry-pick #20396 to 7.x: [Filebeat][SophosXG Module] Renaming module and fileset

[adriansr]

Cherry-pick of PR #20396 to 7.x branch. Original message:

What does this PR do?

Renaming module from SophosXG to Sophos, and fileset from firewall to XG.

This allows us to easier add more fileset under the more generally named Sophos module

Why is it important?

Makes adding new filesets to Sophos easier and cleaner.

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.

Author's Checklist

Module already has a PR Changelog entry, and has not been released yet, so removing the checkbox for changelog

Updated golden files with:

MODULES_PATH=$PWD/module GENERATE=1 INTEGRATION_TESTS=1 BEAT_STRICT_PERMS=false TESTING_FILEBEAT_MODULES=sophos nosetests -v -s tests/system/test_xpack_modules.py

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Pinging @elastic/siem (Team:SIEM)

[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request #20408 updated]

• Start Time: 2020-08-03T17:21:33.226+0000

• Duration: 58 min 11 sec

Test stats 🧪

Test	Results
Failed	0
Passed	5504
Skipped	824
Total	6328