feat: add extended course block dimension table (FC-0051)

[SoryRawyer]

This change introduces another dimension table, dim_course_blocks_extended, which includes the section and subsection names to which each block belongs. This is included as a separate model instead of adding onto dim_course_blocks so as to avoid any unnecessary joins when a model requires block metadata but does not need the extra information joined into dim_course_blocks by this new model.

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[SoryRawyer]

Since a lot of the engagement charts need to be filtered by section and subsection name I felt it would be helpful to have this model, while at the same time I felt that there were enough models that don't need this information that it would be better to build a separate model instead of adding to the existing one. If this seems too confusing then I'd be happy to consolidate everything into dim_course_blocks.

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