fix: map policy properties to contract request

[ronjaquensel]

What this PR changes/adds

Maps properties, when an IDS ContractOffer is mapped to an IDS ContractRequest.

Why it does that

To allow sending additional policy properties to the provider during the contract negotiation.

Linked Issue(s)

Closes #1901

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• assigned appropriate label? (exclude from changelog with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)