[Frontend] update workflow and package mgr for monorepo config

[Jennievon]

Why this change is needed

This PR migrates the frontend applications from npm to pnpm to improve package management and test the monorepo configuration setup. The updates include:

• Switching from npm to pnpm for package management, optimising install speed and disk space usage
• Adjusting the CI/CD workflow to reflect this package manager change

The migration to pnpm helps achieve better performance with workspace features and provides a way to adequately test the monorepo configuration setup for Tenscan, Gateway, and the Bridge visually before merging. Also, the monorepo structure will facilitate better collab and more efficient dependency mgt across the codebase

Issue: #3948

What changes were made as part of this PR

• updated package.json scripts to use pnpm.
• updated frontend workflows and Dockerfile to align with the new package manager.
• configured workspace settings for monorepo support.

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[BedrockSquirrel]

LGTM - might be good to try deploying in dev from this branch before merging though just to make sure we don't break deployments from main

[Jennievon]

This PR removes npm support and fully migrates to pnpm. The current Dockerfile only supports npm, so it will need updating for pnpm compatibility before testing deployment in dev. I will need to merge this in and then test the monorepo config on dev.