Rename /entities:search API

[Aescwine]

Related to this issue: https://github.com/OriginTrail/ot-node/issues/1758, would it make more sense to change the /entities:search API to better reflect it's use, which is for searching for assets?

/entities:search -> /assets/search

This way the asset API routes would have more of a logical association and be more user friendly:

/assets/provision/
/assets/provision/result
/assets/update/
/assets/update/result
/assets/search/
/assets/search/result

https://github.com/OriginTrail/ot-node/blob/f67952dd973883398b76a014d9274884b2ed6243/modules/controller/rpc-controller.js#L377