Enable Wallet data model validation

[rolsonquadras]

Currently system doesn't validate JSON-LD contexts (disabled using config). This needs to be enabled and along with fix all the contexts issues. Also, remove example.org from context as it's not valid base.

Reference:

• https://github.com/hyperledger/aries-framework-go/pull/3261
• https://github.com/trustbloc/agent-sdk/blob/main/cmd/wallet-js-sdk/docs/data_models.md