Feature(database): implement defined database structure into Prisma schema

[AlfredoPrograma]

What

• Implement core database relationships in Prisma Schema
• Add npm run db:push command to push
• Add DATABASE_URL environment variable to .env.example file

How

• Append Tasks and Workspaces properties to User table
• Create Workspace entity
• Create Task entity
• Create TaskStatus enum
• Create UsersOnWorkspaces pivot table with admin metadata

Extra notes

• Database diagram reference

[juanzenn]

Add to the tasks model an onDelete directive when workspaces are deleted