[Filebeat] Add access_key_id, secret_access_key and session_token into aws module config

[kaiyan-sheng]

What does this PR do?

This PR is to add missing configuration parameters into filesets under aws module.

Why is it important?

With this PR, users will be able to use access_key_id, secret_access_key and session_token directly in Filebeat aws module.

This PR also adds the missing config for ec2 fileset into default aws.yml.disabled config with enabled: false.

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.

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[leehinman]

This is great and offers a lot of flexibility for our users.

I'm wondering if we should add an authentication section to the docs to explain what happens when the various auth variables are set and what combo to use them in? The s3 input docs already has the "aws-credentials-config" section. Could we maybe link to that?

[kaiyan-sheng]

@leehinman Good point! I will add the link. Thank you!

[leehinman]

LGTM