Add GetAWSCredentials function in libbeat common

[kaiyan-sheng]

This PR creates a function in libbeat common to get aws credentials. If access_key_id and secret_access_key are given, then these will be used as aws credentials to make API calls. If they are not given, then this function will load default aws config instead from ~/.aws/credentials for Linux & Mac or %USERPROFILE%\.aws\credentials for Windows. This PR also introduced a new config parameter credential_profile_name. It gives GetAWSCredentials function the ability to load aws config from a specific profile. Please see https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-profiles.html for more details.

This function is from #12701 and I realized both metricbeat and filebeat will need this. That's why I'm moving this method to libbeat common. Also functionbeat will be able to use it.

closes: #12708

How to test it

In order to test GetAWSCredentials, you can use aws Metricbeat module or aws Filebeat module:

• For aws module, change aws.yml to use credential_profile_name:

- module: aws
  period: 300s
  credential_profile_name: <profile name>
  metricsets:
    - ec2
  regions:
    - us-east-1

• Make sure valid aws credentials are stored in ~/.aws/credentials under
• Start metricbeat and aws module should run just fine with reading credentials from the profile in ~/.aws/credentials file.
• You can test this by putting aws credentials under a specific or under default. If it's under default, then credential_profile_name: default is not needed.

[kaiyan-sheng]

@kvch @andrewvc This PR created a common function to get AWS credentials in x-pack/libbeat. Will this be useful to functionbeat? I see we can probably use this at https://github.com/elastic/beats/pull/12401/files#diff-d30e2477c79a898c9f035f2980beb071R55 in @andrewvc's PR for adding auto discover provider for AWS ELB.

[dedemorton]

The changes I've suggested should get your docs building locally. Just reach out to me if you have more issues. After you have the structure like you want it, we'll need to update the sources section in the conf.yaml so the full doc build can find the new libbeat directory under x-pack. See https://github.com/elastic/docs/blob/master/conf.yaml#L731.

[exekias]

Looking good overall, I would love input from @andrewvc @kvch // @ph to see if we can get a similar behavior across the board

[kaiyan-sheng]

jenkins, test this please

[andrewvc]

Code LGTM, good stuff! Left some minor corrections for the docs/copy.

Looking forward to using this in #9043 .

[andrewvc]

LGTM

[kaiyan-sheng]

CI failure is not related: #13009

[kaiyan-sheng]

This PR broke docs CI. When merging this PR into 7.x, https://github.com/elastic/docs/blob/master/conf.yaml#L745 needs to be changed again, 7.x needs to be removed from the list of excluded branches.

[kaiyan-sheng]

Done updating the description with how to test this. Thanks for adding the label @andresrc !