adding option to set max threshold

[alexhans1]

Hi there,

In our org we would like to set a max value for coverage. Meaning if the coverage is above that value, we no longer bump the thresholds.
This ensures that we set realistic targets that we don't have to adjust downwards all the time.
This would also fix issue #21

This PR adds this ability to jest-it-up.

How it works:

current:

coverageThreshold: {
  global: {
    statements: 60,
    branches: 12,
    functions: 32,
    lines: 34,
  },
}

actual:

coverageThreshold: {
  global: {
    statements: 62,
    branches: 45,
    functions: 70,
    lines: 55,
  },
}

npx jest-it-up --max-threshold 60

new:

coverageThreshold: {
  global: {
    statements: 60,
    branches: 45,
    functions: 60,
    lines: 55,
  },
}

please review it and consider merging it, if you think it adds value.

[rbardini]

What do you think of renaming it target threshold? Should avoid the min vs max confusion. Also with a short -T flag:

Suggested change

	'--max-threshold <max>',
	'max value to update the threshold',
	'-T, --target <threshold>',
	'target threshold to reach',

[alexhans1]

done

[rbardini]

Please run jest-it-up --help and paste the output here so that the docs match.

[alexhans1]

done

[rbardini]

Can't we skip updating if nextCoverage is greater than maxThreshold instead?

Suggested change

	if (nextCoverage > threshold + margin) {
	const next = Math.min(nextCoverage, maxThreshold ?? 100)
	if (nextCoverage > threshold + margin && nextCoverage <= maxThreshold) {

[alexhans1]

not quite. if the nextCoverage is bigger than the targetThreshold, then we still want to update it to the targetThreshold.

But if the previous threshold was already the target threshold, then we don't need to update it. I added that condition.