Implement API for Operational Learning statistics

[samshara]

This API must also support all filters applicable to the Operational Learning page.
The response should return the following fields:

• operations_included: Total count of operations based on the applied filters.
• sources_used: Count of unique sources referenced in the learning data.
• learning_extracts: Total number of validated learning extracts.
• sectors_covered: Count of distinct sectors covered.
• sources_overtime: Year-wise breakdown of sources used, categorized by type:
  • DREF
  • Emergency Appeal
  • International Appeal
  • Forecast-Based Action (FBA)
• learning_by_region: Learning data grouped by region:
  • region_id: Region ID
  • region_name: Region name
  • count: Number of learning extracts for the region.
• learning_by_sectors: Learning data grouped by sectors:
  • sector_id: Sector ID
  • sector_name: Sector name
  • count: Number of learning extracts for the sector.
• learning_by_country: Learning data for map visualization, grouped by country:
  • country_id: Country ID
  • country_name: Country name
  • learning_count: Number of learning extracts in the country.