Add index to mod_logger.log_table for help with better query planning

[eiffel777]

Adding this index help the query planner to pick the correct index for sql queries that are trying to find the most recent run of a value in the ident column in the mod_logger.log_table. An example query is below.

SELECT id, logtime, priority, message FROM log_table WHERE ident = 'xdmod-ingestor' AND priority = '5' AND message LIKE '%\"process_start_time\":%' ORDER BY id DESC LIMIT 1

This index has been added to metrics-dev

Tests performed

Tested in docker, metrics-dev, and metrics-staging

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