chore(go.d/ddsnmp): add index-based tags and cross-table index transformation support

[ilyam8]

Summary

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[Copilot]

Pull Request Overview

This PR introduces support for index-based tags and cross‐table index transformation in the SNMP collector by refactoring the table walking and processing logic.

• Removed the previous table-skipping logic for tags with index transformations.
• Updated the processTableData function to apply index transformations and handle index‐based tags.
• Added helper functions (getIndexPosition and applyIndexTransform) and refined SNMP walk processing.

Comments suppressed due to low confidence (2)

src/go/plugin/go.d/collector/snmp/ddsnmp/ddsnmpcollector/collect_table.go:266

• [nitpick] Ensure that the 'ternary' function is defined or imported in the codebase, as Go does not provide a built-in ternary operator. Consider refactoring this into a clear if/else block if there is any ambiguity.

tagName := ternary(tagCfg.Tag != "", tagCfg.Tag, fmt.Sprintf("index%d", tagCfg.Index))

src/go/plugin/go.d/collector/snmp/ddsnmp/ddsnmpcollector/collect_table.go:470

• The revised snmpWalk function no longer logs each non-data PDU as missing; instead, it marks the entire oid as missing when no valid PDUs are found. Please confirm that this logging change is intentional for diagnostic purposes.

if isPduWithData(pdu) {