Add ability to configure allowed number of missed lines per target

[vlad-ko]

What product do you want to improve?
Codecov config

Is your feature request related to a problem? Please describe.
A customer would like to be able to miss X number of lines on a given PR.

Describe the solution you'd like
ideally we'd have some sort of combination. The same way that threshold takes the "real" target and lets you pass an otherwise "failed" check in limited, well defined scenarios... adding a min_lines_missed could let us set our target at a good spot 85%, but if you miss only a few lines, it still doesn't fail the PR check:

hypothetical setup of target: 85%, min_lines_missed: 4

• 50 line PR, 5 lines missed -> passes, because 90% > target of 85%
• 50 line PR, 10 lines missed -> fails, because 80% < target of 85%, and 10 lines > 4
• 5 line PR, 1 lines missed -> passes, because even tho 80% < target of 85%, only missing 1 line is under the threshold of 4
• 5 line PR, 5 lines missed -> fails, because 0% < target of 85%, and 5 lines > 4