metrics: rename memory enrichment table counters to end with _total

Summary

Three counter metrics in the memory enrichment table are missing the _total suffix, violating the instrumentation spec.

From docs/specs/instrumentation.md: "Counters MUST end with total"

Metrics to rename

Current name	Correct name
memory_enrichment_table_failed_insertions	memory_enrichment_table_failed_insertions_total
memory_enrichment_table_failed_reads	memory_enrichment_table_failed_reads_total
memory_enrichment_table_ttl_expirations	memory_enrichment_table_ttl_expirations_total

These are defined in lib/vector-common/src/internal_event/metric_name.rs as CounterName variants. Their descriptions already say "The total number of..." confirming the intent was to follow the _total convention.

Notes

These are breaking changes for anyone scraping these metrics directly. The old names should be kept as deprecated aliases or the rename should be accompanied by a changelog entry.