Avoid broken aggregation (#95)

⚠️ this PR requires a proper review. I'm not 100% sure it will not brake things.

It will help to avoid having a `must` key outside of `bool` context.
Example:

Before a fix:
```
{
    "query": {
        ...
    },
    "aggs": {
        "topics": {
            "filters": {
                "filters": {
                    ...
                    "bool": {
                        "must": {
                            "bool": {
                                "must": [
                                    {
                                        "query_string": {
                                            ...
                                        }
                                    }
                                ]
                            }
                        }
                    }
                }
            }
        }
    }
}
```
which cause a
```
"caused_by": {
            "type": "named_object_not_found_exception",
            "reason": "[87:33] unknown field [must]"
        }
```

after the fix:
```
{
    "query": {
        ...
    },
    "aggs": {
        "topics": {
            "filters": {
                "filters": {
                    ...
                    "query": {
                        "bool": {
                            "must": [
                                {
                                    "query_string": {
                                        ...
                                    }
                                }
                            ]
                        }
                    }
                }
            }
        }
    }
}
```

Initial query provided to `fix_query`:

```{'query': {'bool': {'must_not': [{'term': {'type': 'composite'}}, {'constant_score': {'filter': {'exists': {'field': 'nextversion'}}}}], 'must': [{'term': {'_id': 'foo'}}], 'should': [], 'filter': [{'bool': {'must': [{'term': {'_type': 'items'}}]}}]}}, 'aggs': {'topics': {'filters': {'filters': {'created_to_old': {'bool': {'must': [{'range': {'versioncreated': {'lte': '2017-01-01T23:59:59+0000'}}}]}}, 'created_from_future': {'bool': {'must': [{'range': {'versioncreated': {'gte': '2020-09-17T04:00:00+0000'}}}]}}, 'filter': {'bool': {'must': [{'terms': {'genre.name': ['other']}}]}}, 'query': {'bool': {'must': [{'query_string': {'query': 'Foo', 'default_operator': 'AND', 'lenient': True}}]}}}}}}, 'size': 0}```

.gitignore

@@ -1,6 +1,7 @@
 *.py[co]
 
 # env
+.python-version
 /env
 /venv
 /bin

eve_elastic/elastic.py

@@ -216,7 +216,7 @@ def fix_query(query, top=True, context=None):
         elif key == "query_string":
             new_query[key] = val
             val.setdefault("lenient", True)
-        elif key == "query" and not top:
+        elif key == "query" and not top and context != "aggs":
             new_query["bool"] = {"must": fix_query(val, top=False, context=context)}
         elif top:
             new_query[key] = fix_query(val, top=False, context=key)