improve(go.d/snmp): add manual_profiles option

[ilyam8]

Summary

This PR adds a new configuration option, manual_profiles, to the SNMP collector.

Problem:

• Some rare devices (e.g. certain printers) do not provide a sysObjectID, making it impossible to apply SNMP profiles automatically. Until now, these devices could not benefit from profile-based metric collection.

Solution:

• Added manual_profiles config option (array of profile names).
• Profile names should be given without file extensions (e.g. generic-device, not generic-device.yaml).
• When sysObjectID is missing and no automatic match is possible, the collector falls back to applying the profiles specified in manual_profiles.
• If both sysObjectID matching and manual_profiles are unavailable, no profiles are applied.

Test Plan

Additional Information

For users: How does this change affect me?

[Copilot]

Pull Request Overview

This PR adds a manual_profiles configuration option to the SNMP collector to enable profile-based metric collection for devices that don't provide a sysObjectID (such as certain printers).

• Added manual_profiles array field to the Config struct for specifying fallback profiles
• Modified profile selection logic to use manual profiles when sysObjectID is empty
• Updated test cases and configuration examples to demonstrate the new functionality

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/go/plugin/go.d/collector/snmp/config.go	Added ManualProfiles field to Config struct
src/go/plugin/go.d/collector/snmp/collect.go	Updated profile setup to pass manual profiles parameter
src/go/plugin/go.d/collector/snmp/ddsnmp/profile.go	Modified FindProfiles function to handle manual profile fallback logic
src/go/plugin/go.d/collector/snmp/ddsnmp/profile_test.go	Added test case and updated function calls for manual profiles
src/go/plugin/go.d/collector/snmp/config_schema.json	Added JSON schema definition for manual_profiles configuration
src/go/plugin/go.d/collector/snmp/testdata/config.yaml	Added test configuration example
src/go/plugin/go.d/collector/snmp/testdata/config.json	Added JSON test configuration example

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[ilyam8]

cc @ralphm