[WIP] plug gravatar field on api

                            
|Q            |A           |
|---          |---         |
|Bug Fix?     |no          |
|New Feature? |yes         |
|BC Breaks?   |no          |
|Deprecations?|no          |
|Tests Pass?  |yes         |
|Fixed Tickets|#JOINDIN-464|
|License      |MIT         |
|Doc PR       |            |
                            


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Todo:

- [x] plug field on user resource 
- [ ] plug field on the comments talk and even resources
i like @lornajane  and @akrabat so i will remove the space between if and ( in the following commit