JEXL. Add: Calculated attributes

[mapedraza]

Is your feature request related to a problem / use case? Please describe.
Have calculated attributes using JEXL, having as value the expression evaluation result.

Describe the solution you'd like

When an attribute type is Calculated the value returned when queriying (and also, when notifiying) should be the expression result.

Provision

{
  "id": "Room2",
  "type": "Room",
  "temperature": {
    "value": 21,
    "type": "Float"
  },
  "kelvin": {
    "value": "${temperature+273}",
    "type": "Calculated"
  }
}

Describe alternatives you've considered
#4579

Describe why you need this feature

• To approach a new use case.
• To improve or simplify an scenario.

Additional information

• What happens when using that attribute within a notification condition?
• Probably, a new URL param should be included to request entities without rendering calculated values (to check if the expression works or not). Another alternative is to change the type.

[fgalan]

Probably, a new URL param should be included to request entities without rendering calculated values (to check if the expression works or not). Another alternative is to change the type.

E.g.

GET /v2/entities?options=plain

[mapedraza]

Probably related #3815

[mapedraza]

Noted by @mrutid : Those attributes need to be manually provisioned one by one in each entity (since data provider is not going to create those attributes). No existing clases or patterns that apply to all the entities, like the case of subscriptions, that is a group provision.