Fix standard json requests without optimizer

[rimrakhimov]

If we send the following standard json request to smart-contracts verifier it fails with error content is not valid standard json: missing field 'optimizer' at line 10 column 3:

{
  "language": "Solidity",
  "sources": {
    "A.sol": {
      "content": "pragma solidity ^0.6.8; contract A {}"
    }
  },
  "settings": {
    "remappings": []
  }
}

The problem is in settings.optimizer field which is not present in the input and is required in our current implementation. But according to solidity documentation (https://docs.soliditylang.org/en/v0.8.15/using-the-compiler.html#input-description), that field should be optional. Thus, in general, we should accept that input and consider it the same way as if we have

{
  "language": "Solidity",
  "sources": {
    "A.sol": {
      "content": "pragma solidity ^0.6.8; contract A {}"
    }
  },
  "settings": {
    "remappings": [],
    "optimizer": {}
  }
}