[rush-migrate-subspace-plugin]: add new plugin

[pedro-gomes-92]

Basic Checks

Have you run rush change for this change?

• Yes
• No

If No, please run rush change before, this is necessary.

If adding a new feature, the PR's description includes:

• Reason for adding this feature
• How to use
• A basic example

Does this PR introduce a breaking change? (check one)

• Yes
• No

If yes, please describe the impact and migration path for existing applications:

Summary

Rush plugin to migrate an existing project into a subspace.

Detail

The rush subspace is a new feature that intends to move common projects into 1 workspace. Teams that want to take advantage of this feature need to manually migrate these projects. This script automates most of these required steps to speed up the migration process.

How to test it

rush migrate-subspace

[CLAassistant]

All committers have signed the CLA.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

---

pedro.gomes seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you have already a GitHub account, please add the email address used for this commit to your account.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}