[Automatic Import] Move "Download" button one step before

[ilyannn]

Context

After generating and adding the integration one can download it as a .zip package.

However, the user might be hesitant to install an integration before reviewing it or they might not have enough permissions to do that (see #198233). Or the user might want to create an integration in a separate cluster for licensing or isolation reasons, and not install it there.

Suggestion

We can move the "Download package button" to the previous step. The actual zip file is produced by a call to our backend using runBuildIntegration so we can do this separately from a call to runInstallPackage.

[elasticmachine]

Pinging @elastic/security-scalability (Team:Security-Scalability)

[ebeahan]

We can move the "Download package button" to the previous step.

I agree that users should have the option to download the .zip without being required to install the package.