feat: Ability to delete account for administrators (#1874)

## Description

Add account delete option in the user account settings.

Fixes #1555 

## Type of change

- [ ] New feature (non-breaking change which adds functionality)


![image](https://user-images.githubusercontent.com/40784971/110349673-edcc5200-8058-11eb-8ded-a31d15aa0759.png)

![image](https://user-images.githubusercontent.com/40784971/110349778-0c324d80-8059-11eb-9291-abfbffedde5e.png)


## Checklist:

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my own code
- [ ] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: Sojan Jose <sojan@pepalo.com>
Co-authored-by: Sojan Jose <sojan.official@gmail.com>
Co-authored-by: Muhsin Keloth <muhsinkeramam@gmail.com>

app/dashboards/account_dashboard.rb

@@ -81,7 +81,8 @@ class AccountDashboard < Administrate::BaseDashboard
   COLLECTION_FILTERS = {
     active: ->(resources) { resources.where(status: :active) },
     suspended: ->(resources) { resources.where(status: :suspended) },
-    recent: ->(resources) { resources.where('created_at > ?', 30.days.ago) }
+    recent: ->(resources) { resources.where('created_at > ?', 30.days.ago) },
+    marked_for_deletion: ->(resources) { resources.where("custom_attributes->>'marked_for_deletion_at' IS NOT NULL") }
   }.freeze
 
   # Overwrite this method to customize how accounts are displayed