Add input to delete .nojekyll and CNAME files

[EndBug]

While in a normal use case keeping .nojekyll and CNAME files is really useful (#354), there are some instances where it would be really nice to just have an option to disable these two checks without having to checkout the gh-pages branch, remove the whole directory, and re-checkout the original branch

github-pages-deploy-action/src/git.ts

Lines 173 to 184 in db399db

	!fs.existsSync(
	`${action.folderPath}/${DefaultExcludedFiles.CNAME}`
	)
	? `--exclude ${DefaultExcludedFiles.CNAME}`
	: ''
	} ${
	!fs.existsSync(
	`${action.folderPath}/${DefaultExcludedFiles.NOJEKYLL}`
	)
	? `--exclude ${DefaultExcludedFiles.NOJEKYLL}`
	: ''
	}`

Related: rossjrw/pr-preview-action#15