Add skip_covered to [html] config

[ryboe]

Is your feature request related to a problem? Please describe.
We can set skip_covered = true in the [report] section of a config file, but the setting is strangely missing from [html].

Unrecognized option '[tool.coverage.html] skip_covered=' in config file pyproject.toml

Instead, I have to pass it as a flag.

coverage html --skip-covered

Describe the solution you'd like
I'd like to be able to write this in pyproject.toml.

[tool.coverage.html]
skip_covered = true

Describe alternatives you've considered
N/A

Additional context
N/A

[nedbat]

Duplicate of #1090. Something is in the air....