Generate workflow summary report for MG7 cross-section checks

[theoheimel]

• generate a table with the results from all the MG7 cross-section checks, including relative deviations and pulls
• provide error messages extracted from the log file below the table
• new verbosity mode auto in MG7 to automatically switch between log and pretty depending on whether a terminal is attached to stdout

See example output here: https://github.com/MadGraphTeam/MadGraph7/actions/runs/29644502579