Update client to use API with mongo functionalities about alerce_client

[ASHuenchuleo]

For the interface, I think it's a good idea to just use the same JSON you would use for a curl request for simplicity:

from alerce.core import Alerce
alerce = Alerce()

query = {
"collection": "detections",
"filter": {
"oid": "ZTF1"
},
"sort": { "mjd": 1 },
"limit": 10
}
detections = Alerce.mongo_find(query, pandas=True)

[ASHuenchuleo]

The client must be able to send queries to this API following these steps

• Add new superclass for ALeRCE client for MongoDB requests
• Add code for parsing the API response
• Implement the following verbs
• • find
• • findOne
• • Aggregate
• Add the option to increase timeout for db gateways
• Add extra functionalities
• • Count

Should we validate the input in every verb or just let the program fail?