Report endpoints accepting form data and other improvements

[1.6]

Added

• Coverage report and genes coverage overview endpoints now accept also requests with application/x-www-form-urlencoded data
• Allow system admin to customise coverage levels to be used in reports' metrics by editing the REPORT_COVERAGE_LEVELS in .env file
• Documentation on how to change app's default coverage level values to be used when creating the reports

Changed

• Templates form submit data as application/x-www-form-urlencoded without having to transform it into json
• Customize form on report page now accepts genes as Ensembl IDs or HGNC symbols

Fixed

• Faster genes overview report loading
• Broken GitHub action due to d4tools failing to install using cargo
• Broken Codecov upload step in GitHub action failing due to missing token
• Completeness cutoff select not updating after submitting customize form on report page