Reduce number of SQL queries in Profiles::SlacksController#edit

What does this MR do?

When we pass the whole projects array to the ServicesHelper, Rails attempts to serialize the whole project object along with its relations. Notably project_import_data and tags cause a bunch of N+1 queries. By manually serializing the project object and explicitly calling only the attributes we need, the number of SQL queries is reduced considerably.

On my local, the number of SQL queries go from 50 queries down to 11.

Screenshots (strongly suggested)

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Related to #21044 (closed)