agent: implements logic to register agents and scan images and upload reports

[ashwiniag]

closes
#91

Introduces

• modularize registry registry: modularize registry #92
• modularize scanner scanner: introduce scanner field and modularize scanner #93
• introduces scanner field in scans and policies tables and updates its API
• updates the GET call of agentTasks to query by status i.e. <enpoint>?status=pending
• updates the scan.Report to hold the json.RawMessage{} i.e scanned reports logic: report server implimentation #94
• updates enum status across tables with respective values
• adds agent registration and polling. You can start agent which gets registered to server and starts polling for its, in its own environment. Command example agent: registeration #76

./gokakashi agent start --server=http://localhost:8000 --token=letsdoit --workspace=/tmp

• adds agent task execution logic.

Abstract Task Execution Flow #77

1. start an agent via cmd
2. make an API call to agent table and register the agent with agent.status = connected
3. start polling for the tasks from agentTasks table where agenttasks.Status = pending and from the order returned in asc of agenttasks.Created_at
   1. picks a task from list
   2. updates the agenttasks.Status = in_progress
   3. fetchScan details using scanID
   4. fetchIntegration details
   5. authenticateAndPullImage
   6. update scan.status = scan_in_progress
   7. perform scan of image with provided scan.scanner
      1. if fails update scan.Status = error
   8. upload report to scan.Report and set scan.Status = complete
      1. if fails update scan.Status = error
   9. updates the agenttasks.Status = complete
4. Continue to next tasks
   No pending tasks. Retrying after 10 seconds