chore: use pnpm in place of lerna

[cabljac]

This PR replaces the outdated and deprecated lerna methods with pnpm.

It also fixes a bunch of npm vulnerabilities, and updates some versions.

TODO:

• Make sure use of pnpm doesn't break release process
• Regression testing before we release things (to check version bumps of packages haven't introduced errors

[cabljac]

CI is failing as it relied on lerna. need to switch to pnpm scripts.

[cabljac]

CI for testing also needs to use npm probably or something? pnpm doesn't create node_modules where we need it for extensions

[Salakar]

woops