Support persistent cache

[mvhirsch]

Webpack 5 introduced persistent (filesystem based) cache, which speeds up build performance in CI by ... a lot.
This plugin forces my setting always to be false, rendering my cache setup useless in CI.

https://webpack.js.org/guides/build-performance/#persistent-cache

Webpack/Grunt Configuration (webpack.config.js, webpack part of Gruntfile.js)

{
    options: {
        cache: {
            type: 'filesystem',
            cacheDirectory: path.resolve('<%= paths.cache %>/webpack')
        }
    }
}

Expected Behavior

A cached output on destination

Current Behavior

No output

Possible Solution

Context

Your Environment

software	version
webpack	5.89.0
grunt-webpack	6.0.0
grunt	1.5.3
node	14.21.3
npm	6.14.18
Operating System	Fedora 39 - 6.8.9-200.fc39.x86_64 GNU/Linux

[mvhirsch]

Looks like unless I want to watch: true (on build servers I usually don't want to watch ...) it's impossible to use build-cache using this module.

grunt-webpack/src/options/WebpackOptionHelper.js

Lines 22 to 26 in 080fa7d

	if (!options.watch) {
	// ensure cache is disabled in non watch mode, as we add our own CachePlugin to support
	// multiple targets in one run with different caches
	options.cache = false;
	}

[alexander-akait]

/cc @danez friendly ping, we should do it, cache is pretty stable