feat: configure colors of output with env variables

[hamskerpir]

Hey,
my usecase was that color that I was using for my terminal prompt is same that is hardcoded in yq, so I've decided add a bit of flexibility to the tool.
Unfortunately, I did not find a config structure, and if it does not exist, I think I'm not the person that should set such change in repository :D

Anyway, here is my small changes to configure output via env vars.

[hamskerpir]

[mikefarah]

I agree with @ccoVeille comments 👍🏼

[hamskerpir]

sorry for long inactivity

[ccoVeille]

I tend to prefer code with less branches

Suggested change

	for envVar, configField := range colorMappings {
	if colorStr := os.Getenv(envVar); colorStr != "" {
	if attr, err := parseColorAttribute(colorStr); err == nil {
	*configField = attr
	}
	}
	}
	for envVar, configField := range colorMappings {
	colorStr := os.Getenv(envVar)
	if colorStr == "" {
	continue
	}
	attr, err := parseColorAttribute(colorStr)
	if err != nil {
	continue
	}
	*configField = attr
	}

Also, I feel like it could be frustrating for someone if they try to use an unsupported value, they won't know it failed. I would report the error to user