feat: default template version based on cli major

[janoshrubos]

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What is the current behavior?

What is the new behavior?

ns create will use the same template major version as the CLI.

Fixes #5515.

[NathanaelA]

Looks good! LGTM.

[rigor789]

@NathanaelA we were just wondering if it's worth backporting, since either way requires a CLI update. The ns8 CLI should be backwards compatible with 6.5.x+ projects, so for most people it's recommended to update and use latest - and for those who want to create an older project, the explicit version has to be passed when creating (@^7.0.0 for example).