Add Basic Authentication documentation and enhance InfluxDB migration auth guide

[KanavCode]

Changes Made

New Documentation

• Basic Authentication Page (operations/basic-auth.md)
  • Complete configuration guide with server.conf examples
  • Client integration examples for all supported languages

Enhanced Documentation

• InfluxDB Migration Guide (guides/influxdb-migration.md)
  • New authentication migration section
  • Configuration matrix comparing InfluxDB vs QuestDB auth
  • Step-by-step migration process with code examples
  • Security considerations for production environments

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