Update agent config defaults and format

[aphralG]

Proposed changes

Fixed defaults and formatting for the client portion of agent config:

• Renamed Common Settings struct to BackOff and moved into to the Client struct
• Created HTTP struct for the Client HTTP config settings
• GRPC config settings are now in the Client Struct
• Set Defaults for KeepAlive and HTTP settings in Client - Made sure defaults were being used for client settings

Client section of the agent config below works and defaults are set to the values below.

client: 
  http:
    timeout: 10s                      # HTTP client timeouts
  grpc:
    keepalive:
      timeout: 10s                   # Client timeout
      time: 20s                      # Total time for client requests
      permit_without_stream: true    # Allow connections without streams
    max_message_size: 1048576        # Max size for client messages (in bytes)
    max_message_receive_size: 1048576 # Max size for receiving client messages
    max_message_send_size: 1048576   # Max size for sending client messages
  backoff:
    initial_interval: 500ms         # Initial backoff interval
    max_interval: 10s                # Maximum backoff interval
    max_elapsed_time: 30s           # Maximum time spent on retries
    randomization_factor: 0.5       # Factor for randomizing the backoff interval
    multiplier: 1.5                 # Backoff multiplier

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[dhurley]

For the Subscribe & CreateConnection RPCs, we always want to retry indefinitely. Otherwise if we stop retrying then the agent will just keep running doing nothing and never connect to the management plane.

Hence why the MaxElapsedTime is set to 0 for these RPCs.