Feature/18 user attribute service

[Sachinbisht27]

#18

Please complete the following steps and check these boxes before filing your PR:

Types of changes

• Bug fix (a change which fixes an issue)
• New feature (a change which adds functionality)

Short description of what this resolves:

• Handling all custom field data from the Glific webhook.
• Creating a new entry for every new custom field.
• Added the logic to update the same entry again once the user changes or updates the details.
• Added the check not to create multiple entries for the same contact field for a user.

Checklist:

• I have performed a self-review of my own code.
• The code follows the style guidelines of this project.
• The code changes are passing the CI checks
• I have documented my code wherever required.
• The changes requires a change to the documentation.
• I have updated the documentation based on the my changes.
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.