Move DeckhouseRelease manifests generation step earlier in d8 mirror pull #185

Use case. Why is this important?

Currently, when running:

d8 mirror pull <bundle> --license <TOKEN> --since-version <VERSION>

the step Generating DeckhouseRelease manifests is executed after pulling all release channels and installers. For large bundles, this means waiting before the file deckhousereleases.yaml appears, even though it depends only on release-channel metadata.

This behavior makes it inconvenient to: quickly obtain deckhousereleases.yaml, generate release manifests.

Proposed Solution

Move the Generating DeckhouseRelease manifests step up in the execution order:
Generate deckhousereleases.yaml immediately after pulling release channels, before pulling heavy artifacts.