CDDL schema for locks

[td202]

Purpose

Define the CDDL schema used for lock transactions, events and queries.

Changes

• Add 'locks.cddl' defining the schema extensions for locks.
• Update GRPC pointer to include lock queries and events.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.

[allanbrondum]

I think it would be better to merge this together with in a CDDL shared with the access control changes (which are currently in cis-7.cddl)