Refactor Authentication Setup

[kneerose]

Currently, authentication logic for proposals, budget proposals, dReps, users, and ADA Holders is maintained in a single file. To improve modularity and maintainability, it's preferable to separate these into individual files and restructure the Playwright project to include only the necessary authentication setup for each context.

TODO

• Extract dRep authentication logic into a separate dRep.auth.setup.ts file
• Extract proposal discussion authentication logic into proposal-discussion.auth.setup.ts
• Extract budget discussion authentication logic into budget-discussion.auth.setup.ts
• Update the Playwright project structure to load only the required authentication setup files based on context

[mesudip]

Todo
Revalidate that the tests are working after the change.

[kneerose]

• Refactor: Auth setup and Test Structure Improvements IntersectMBO/govtool#3523