filter_kubernetes: add entity attribute retrieval logics

[zhihonl]

Background

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

Problem

For enabling Explore Related experience in AWS EKS cluster, we need additional data such as workload(deployment, daemonset, etc) type, cluster name. There's also an option to associate name of the service running within the cluster but FluentBit doesn't have existing functionality for that.

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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.*
            enable_entity   true
          
          [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
          
          [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

• Debug log output from testing the change

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

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.