GO-6915 Dynamic placeholders for templates

[KirillSto]

https://linear.app/anytype/issue/GO-6915/dynamic-shortcuts-in-relation-default-values-templates-only

Add support of dynamic placeholders in template details:

• add _today and _current_user placeholders for datetime and spaceMember details
• add TemplatePlaceholders hidden system relation for storing placeholder values in details of a template
• add TemplatePlaceholders setting logic on ObjectSetDetails call
• add placeholders resolution logic on object creation flow

[github-actions]

New Coverage	46.3% of statements
Patch Coverage	64.0% of changed statements (48/75)

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