fix: remove useless cols (CM-731)

[ulemons]

PR: Cleanup of redundant fields in Tinybird and addition of a cleaned backup MV

Description

This PR focuses on simplifying the Tinybird data pipeline by removing redundant fields and introducing a new materialized view (MV) for a lightweight backup of the activities datasource.

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What Has Been Changed

• Removed unused or redundant columns from the activities.datasource.
• Updated activities_deduplicated_ds.datasource and its copy-pipe (activities_deduplicated_copy_pipe.pipe) to align with the reduced schema.
• Added a new datasource activities_backup_cleaned.datasource with a simplified structure for backup purposes.
• Created a materialized view activities_backup_cleaned_mv.pipe that populates the cleaned backup from the original activities table.
• Ensured that the backup uses the same engine setup (ReplacingMergeTree, partitioned by year of createdAt, sorted by id) but retains only essential fields for archival and analytics.

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[borfast]

Looks good but there are a few places where you're removing the isContribution flag, which has already been removed (those changes have already been merged), so I would suggest you rebase your branch and check for conflicts that may arise from that. It shouldn't be a big deal, as it's only removing stuff.