chore: add interface to abstract cmd which allows unit testing backends

[leoparente]

This pull request introduces a new abstraction layer for command execution and refactors existing code to use this new abstraction. The changes also include the addition of a mock implementation for testing purposes. The most important changes include the introduction of the CmdInterface, refactoring of multiple backend components to use this interface, and the addition of tests for the OpenTelemetry backend.

Introduction of CmdInterface:

• agent/backend/cmd.go: Added CmdInterface to abstract the functionality of the go-cmd package and implemented CmdWrapper to wrap the cmd.Cmd struct.

Refactoring to use CmdInterface:

• agent/backend/devicediscovery/device_discovery.go: Replaced direct usage of cmd.Cmd with backend.CmdInterface and updated related code. [1] [2] [3] [4] [5]
• agent/backend/networkdiscovery/network_discovery.go: Similar refactoring to replace cmd.Cmd with backend.CmdInterface. [1] [2] [3] [4] [5]
• agent/backend/otel/otel.go: Updated to use backend.CmdInterface instead of cmd.Cmd. [1] [2] [3] [4] [5]
• agent/backend/pktvisor/pktvisor.go: Refactored to use backend.CmdInterface. [1] [2] [3] [4]

Addition of mock implementation for testing:

• agent/backend/mocks/mocks.go: Added MockCmd, a mock implementation of CmdInterface, and helper functions to set up different process states for testing.

Tests for OpenTelemetry backend:

• agent/backend/otel/otel_test.go: Added tests for the OpenTelemetry backend using the new mock implementation.

[github-actions]

Go test coverage

STATUS	ELAPSED	PACKAGE	COVER	PASS	FAIL	SKIP
🟢 PASS	1.03s	github.com/netboxlabs/orb-agent/agent	0.0%	1	0	0
🟢 PASS	0.01s	github.com/netboxlabs/orb-agent/agent/backend	0.0%	0	0	0
🟢 PASS	0.01s	github.com/netboxlabs/orb-agent/agent/backend/devicediscovery	0.0%	0	0	0
🟢 PASS	0.00s	github.com/netboxlabs/orb-agent/agent/backend/mocks	0.0%	0	0	0
🟢 PASS	0.00s	github.com/netboxlabs/orb-agent/agent/backend/networkdiscovery	0.0%	0	0	0
🟢 PASS	2.02s	github.com/netboxlabs/orb-agent/agent/backend/otel	38.3%	1	0	0
🟢 PASS	0.01s	github.com/netboxlabs/orb-agent/agent/backend/pktvisor	0.0%	0	0	0
🟢 PASS	0.01s	github.com/netboxlabs/orb-agent/agent/backend/worker	0.0%	0	0	0
🟢 PASS	1.06s	github.com/netboxlabs/orb-agent/agent/configmgr	47.7%	9	0	0
🟢 PASS	1.01s	github.com/netboxlabs/orb-agent/agent/policies	100.0%	15	0	0
🟢 PASS	1.03s	github.com/netboxlabs/orb-agent/agent/policymgr	70.3%	10	0	0
🟢 PASS	2.50s	github.com/netboxlabs/orb-agent/agent/secretsmgr	51.8%	45	0	0
🟢 PASS	1.01s	github.com/netboxlabs/orb-agent/agent/version	100.0%	1	0	0

Total coverage: 31.5%

[github-actions]

🎉 This PR is included in version 2.0.0 🎉

The release is available on GitHub release

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