aws: add integrations for CloudWatch Explore related feature

[zhihonl]

CloudWatch introduced a new feature called Explored Related which is a UI component that helps user navigate between their telemetry(metrics,logs) and AWS resources. This is done by including a new field in PutLogEvents API which is called Entity. More documentation about this new field can be found here: https://docs.aws.amazon.com/AmazonCloudWatchLogs/latest/APIReference/API_Entity.html

Since FluentBit has a CloudWatch output plugin that emits logs to CloudWatch Logs, this PR adds changes that scrapes information necessary for populating the entity field.

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Enter [N/A] in the box, if an item is not applicable to your change.

Testing
Before we can approve your change; please submit the following in a comment:

• Screenshot of how UI interacts with the changes made in this PR
  

• Example configuration file for the change

application-log.conf: |
          [INPUT]
            Name                tail
            Tag                 application.*
            Exclude_Path        /var/log/containers/cloudwatch-agent*, /var/log/containers/fluent-bit*, /var/log/containers/aws-node*, /var/log/containers/kube-proxy*
            Path                /var/log/containers/*.log
            multiline.parser    docker, cri
            DB                  /var/fluent-bit/state/flb_container.db
            Mem_Buf_Limit       50MB
            Skip_Long_Lines     On
            Refresh_Interval    10
            Rotate_Wait         30
            storage.type        filesystem
            Read_from_Head      ${READ_FROM_HEAD}
          
          [INPUT]
            Name                tail
            Tag                 application.*
            Path                /var/log/containers/fluent-bit*
            multiline.parser    docker, cri
            DB                  /var/fluent-bit/state/flb_log.db
            Mem_Buf_Limit       5MB
            Skip_Long_Lines     On
            Refresh_Interval    10
            Read_from_Head      ${READ_FROM_HEAD}
          
          [INPUT]
            Name                tail
            Tag                 application.*
            Path                /var/log/containers/cloudwatch-agent*
            multiline.parser    docker, cri
            DB                  /var/fluent-bit/state/flb_cwagent.db
            Mem_Buf_Limit       5MB
            Skip_Long_Lines     On
            Refresh_Interval    10
            Read_from_Head      ${READ_FROM_HEAD}
          
          [FILTER]
            Name                aws
            Match               application.*
          
          [FILTER]
            Name                kubernetes
            Match               application.*
            Kube_URL            https://kubernetes.default.svc:443
            Kube_Tag_Prefix     application.var.log.containers.
            Merge_Log           On
            Merge_Log_Key       log_processed
            K8S-Logging.Parser  On
            K8S-Logging.Exclude Off
            Labels              Off
            Annotations         Off
            Use_Kubelet         On
            Kubelet_Port        10250
            Buffer_Size         0
            Use_Pod_Association On
          
          [OUTPUT]
            Name                cloudwatch_logs
            Match               application.*
            region              ${AWS_REGION}
            log_group_name      /aws/containerinsights/${CLUSTER_NAME}/application
            log_stream_prefix   ${HOST_NAME}-
            auto_create_group   true
            extra_user_agent    container-insights
            add_entity          true

• Debug log output from testing the change

• Attached Valgrind output that shows no leaks or memory corruption was found

SUCCESS: All unit tests have passed.
==23696==
==23696== HEAP SUMMARY:
==23696==     in use at exit: 0 bytes in 0 blocks
==23696==   total heap usage: 8,123 allocs, 8,123 frees, 1,344,364 bytes allocated
==23696==
==23696== All heap blocks were freed -- no leaks are possible
==23696==
==23696== For lists of detected and suppressed errors, rerun with: -s
==23696== ERROR SUMMARY: 213 errors from 38 contexts (suppressed: 0 from 0)

If this is a change to packaging of containers or native binaries then please confirm it works for all targets.

• Run local packaging test showing all targets (including any new ones) build.
• Set ok-package-test label to test for all targets (requires maintainer to do).

Documentation

• Documentation required for this feature
  Need to add documentation about new configuration values that enables Explored Related experience for users.

Backporting

• Backport to latest stable release.

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Fluent Bit is licensed under Apache 2.0, by submitting this pull request I understand that this code will be released under the terms of that license.