feat: late initialization of astroport oracle contract #NTRN-429

[foxpy]

List of changes:

• asset_infos field in InstantiateMsg is now optional, and, when this field is not set, contract remains unusable;
• manager field added to InstantiateMsg which sets a contract manager. Contract manager is the only account which can set asset_infos field;
• ExecuteMsg now has two new handles:
  • UpdateManager which is only executable by owner to set a new manager;
  • SetAssetInfos for use by manager in the aforementioned scenario.

Small note for reviewers: schema used to be outdated before I have edited this contract, hence the diff for schema is quite big and mostly unrelated to my patchset.

[Tracking task]

[sotnikov-s]

the rest lgtm

[sotnikov-s]

discussed a couple of things with @foxpy and @ratik that need to be addressed:

1. remove asset_info from init msg because it will always be None in our case;
2. come to a conclusion with @ratik re amount of times the asset_info can be set during the contract's life

thus I renounce the approval