Update assetPluginVersion to v4 (major)

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
com.bertramlabs.plugins:asset-pipeline-gradle	3.4.7 -> 4.4.0
com.bertramlabs.plugins:asset-pipeline-grails	3.4.7 -> 4.3.0

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