Investigate webpack speed-up in MR pipelines

We should have a look whether we can speed up MR pipelines by disabling certain features like minification and compression for example.

Downsides: If default branch and MRs differ too much, we might end up with side-effecty issues.

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The following discussion from !96403 (merged) should be addressed:

• @slashmanov started a discussion: (+1 comment)

  question: can\should we do that for everything that runs in CI\not in a main branch? That could potentially speed up other jobs as well.