agent: implement status command

[glimchb]

this is empty https://github.com/opiproject/sztp/blob/main/sztp-agent/pkg/secureagent/status.go

status command should show where in the onboarding stage the device is right now...
for example: waiting on DHCP response...
or downloading file...
or pending reboot...
or provisioning was already completed...
or something else...

See this example:
https://cloudinit.readthedocs.io/en/latest/howto/status.html

and code https://github.com/canonical/cloud-init/blob/a01b8d31f8364a3d86f016a2940df1b38598889d/doc/status.txt#L4

maybe do do this, we need to create a file on the filesystem, like in example above, in /var/lib/sztp/result.json and in /run/sztp/result.json

[bhoopesh369]

In this should we recreate the /var/lib/sztp/result.json file
or just append to it, by opening in write mode
because there are potential complications with managing partial writes or file corruption. (basically to maintain atomicity)

I think initially writing to a temp file and then replace it with original works?

func SaveResultFile(result *Result, path string) error {
    tempPath := path + ".tmp"
    file, err := os.Create(tempPath)
    if err != nil {
        return err
    }
    defer file.Close()

    encoder := json.NewEncoder(file)
    if err := encoder.Encode(result); err != nil {
        return err
    }

    // Atomic move of temp file to replace the original.
    return os.Rename(tempPath, path)
}

[glimchb]

1. add /var/lib/sztp/result.json as argument to daemon command. this json can be default value
2. add /var/lib/sztp/result.json as argument to status command. this json can be default value
3. every time we doReportProgress you should also save the local state here inside this json
4. sometimes you save local state without sending a report to bootstrap server since report progress is API call to bootstrap see https://www.rfc-editor.org/rfc/pdfrfc/rfc8572.txt.pdf