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/views/mailers/administrator_notifications/account_notification_mailer/account_deletion.liquid

@@ -0,0 +1,16 @@
+<p>Hello,</p>
+
+<p>Your account <strong>{{ meta.account_name }}</strong> has been marked for deletion. The account will be permanently deleted on <strong>{{ meta.deletion_date }}</strong>.</p>
+
+{% if meta.reason == 'manual_deletion' %}
+<p>This action was requested by one of the administrators of your account.</p>
+{% else %}
+<p>Reason for deletion: {{ meta.reason }}</p>
+{% endif %}
+
+<p>If this was done in error, you can cancel the deletion process by visiting your account settings.</p>
+
+<p><a href="{{ action_url }}">Cancel Account Deletion</a></p>
+
+<p>Thank you,<br>
+Team Chatwoot</p>