Add clean steps using rimraf

[kmcginnes]

Description

I noticed there was a clean step in /packages/graph-explorer/package.json and it used rimraf, but rimraf wasn't installed in the devDepencies. So I've added it to both the client and server, with the accompanying node scripts.

Validation

• Run pnpm clean at the root to delete the */dist folders

Related Issues

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0
  license.
• I have run pnpm checks to ensure code compiles and meets standards.
• I have run pnpm test to check if all tests are passing.
• I have covered new added functionality with unit tests if necessary.
• I have added an entry in the Changelog.md.