[receiver/ciscoosreceiver] Add SSH connection implementation

[etserend]

Description

Add SSH connection implementation for the Cisco OS receiver to collect metrics from Cisco devices via SSH.

This PR enhances the receiver with:

• SSH client infrastructure with password/key authentication
• Semantic configuration using device.host.* and auth.* conventions
• Modular scrapers for system and interface metrics
• Complete metadata definitions with generated code
• Proper validation and error handling

Link to tracking issue

#42647

Testing

• Unit tests for config validation, factory, and SSH connections
• All repository checks passing: make generate, make checkdoc, make checkmetadata
• Generated lifecycle tests via mdatagen

Documentation

• Complete README with configuration examples and metrics documentation
• metadata.yaml
• with interface and system metric definitions
• Changelog entry added

[dmitryax]

Is the utilization value returned as a pre-aggregated value from the device or we will be doing the temporal aggregation in the receiver keeping the state between the scrapes?

[etserend]

The device gives current values at each scrape — not a pre-aggregated value. The receiver doesn’t track past data.

[dmitryax]

I mean the utilization typically is a temporally pre-aggregated value over raw CPU time counter. If that's what is returned, we're good. We can reconsider in the implementation if needed

[otelbot]

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