Add template block theme

[stian-overasen]

Add simple minimalistic block theme for new projects to replace the classic dekode-theme theme.

• Basic block theme setup with T2.
• Using default WordPress font sizes and spacing scale out of the box.
• T2 Custom Block Margin v2 setup using default WordPress spacing scale.
• T2 Enqueue Theme Block Styles setup so you can define and load block styling only when needed.
• Some basic styling for blocks to get you started.
• Using T2 Horizontal Header and T2 Footer blocks. (Can easily be replaced with something more advanced)

This theme uses Core Block Spacing which is not fully compatible with T2 Custom Block Margin v2. Read more on this in #511

[github-actions]

Composer package changes

Prod Packages	Operation	Base	Target
dekode/block-theme	New	-	1.0.0

Dev Packages	Operation	Base	Target
squizlabs/php_codesniffer	Upgraded	3.10.1	3.10.2

[stian-overasen]

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