Add UDTF that detects linux kernel header installation and add column to GetAgentStatus

[ddelnano]

Summary: Add UDTF that detects linux kernel header installation and add column to GetAgentStatus

This is a prerequisite to accomplish #2051. The px deploy command uses the GetAgentStatus UDTF in its final healthcheck step. With this kernel header detection in place, the px cli can use the results from the px/agent_status script to print a warning message if kernel headers aren't detected.

The helm install flow needs to be covered as well. My hope is that this UDTF could be used for that use case as well, but I need to further investigate the details of that.

Relevant Issues: #2051

Type of change: /kind feature

Test Plan: Skaffolded to a Ubuntu GKE cluster and tested the following

• Kelvin always reports false as it doesn't bind mount / to /host
• PEM running on host without linux-headers-$(uname -r) package reports false
• PEM running on host with linux-headers-$(uname -r) package reports true

$ gcloud compute ssh gke-dev-cluster-ddelnano-default-pool-a27c1ac2-x5k2 --internal-ip -- 'ls -alh /lib/modules/$(uname -r)/build'

lrwxrwxrwx 1 root root 38 Aug  9 15:25 /lib/modules/5.15.0-1065-gke/build -> /usr/src/linux-headers-5.15.0-1065-gke

$ gcloud compute ssh gke-dev-cluster-ddelnano-default-pool-a27c1ac2-j6pg --internal-ip -- 'ls -alh /lib/modules/$(uname -r)/build'

ls: cannot access '/lib/modules/5.15.0-1065-gke/build': No such file or directory

Changelog Message: Add GetLinuxHeadersStatus UDTF and add kernel_headers_installed column to GetAgentStatus

[ddelnano]

This duplicates a portion of the work done by BCCWrapper. Another option would be to move that header installation here rather than checking for the presence of the headers. That wouldn't suffer from the test drawbacks outlined here.

[ddelnano]

@pixie-io/maintainers this is ready for review when you have the chance!