chore(agent): organized go based agent config and key into dedicated directory

[ltan10]

What kind of change does this PR introduce?

• Bugfix
• New Feature
• Feature Improvment
• Refactoring
• Documentation
• Other, please describe:

Description:

• Organized go based agent config and key files into own dedicated directory in /etc/agent-agent
• Modified default PRIVATE_KEY value for podman, snap and docker installation in shell install script

[otavio]

The biggest problem I foresee here is migrating the field-deployed agents.

So even though I agree with the idea of this change, we need to consider how we will migrate the existing agents to work with this new approach or provide a backward-compatible way for them to keep working.

How do you foresee solving this issue?

[ltan10]

With all the testing. I've stumbled upon this myself.
From what I have seen, the migration is fine. as the install script during the migration from roofts to go based binary for the agents already leave the config.json behind and recreate the the new env config file.

The only persistent remaining file is just shellhub.key

Two methods for transition:

1. Just install/add/upgrade agent as normal using install script as per normal

• New shellhub.key gets regenerated in the new directory and device appears for pending approval.
• Requires user to manually remove existing accepted devices due to hostname clashes and accept the new pending devices
  or

2. Use existing shellhub.key on device by manually transfering it to /etc/shellhub-agent prior to executing install script.

• install script agent upgrade will just use existing key.

@otavio someone should be able to replicate my findings for confirmation.
I have been generally just been using option 1. And have only tested on the standalone deployment.
If someone can verify that i have changed the correct sections for the other installation methods and test, that would be great.