Fix log sampling overrides by running preview processors before filtering

[trask]

Summary

• Add a smoke test (TelemetryProcessorLogFilterSamplingOverridesTest) that reproduces issue Filter logs using attributes does not work starting version 3.7.2 #4526 by exercising sampling overrides based on attributes derived by preview processors.
• Adjust the log filtering pipeline so AzureMonitorLogFilteringProcessor applies preview attribute/log processors before executing severity filtering and sampling overrides, ensuring those overrides see the processed attributes.

Root Cause

• PR #4130 introduced AzureMonitorLogFilteringProcessor, moving severity filtering and sampling overrides from AgentLogExporter to a processor that now runs ahead of preview attribute and log processors.
• Because these preview processors still wrap only the exporter, overrides that relied on attributes they extract (e.g., regex-based fields) were evaluated against unprocessed log records, causing the regression described in issue Filter logs using attributes does not work starting version 3.7.2 #4526.

Fix Details

• Apply preview attribute and log processors inside AzureMonitorLogFilteringProcessor before sampling decisions so overrides can match on transformed attributes.
• Thread the processor configs from SecondEntryPoint into the filtering processor to maintain the prior processing order.