Add a migration guide (#2199)

Motivation:

Moving from 1.x to 2.x isn't trivial. We should provide a guide for
doing this.

Modifications:

- Add a guide for migrating client code and services
- Add a script which can automate parts of this

Result:

Some guidance on migrating.

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Co-authored-by: Gus Cairo <[email protected]>

Author: glbrntt