Add more icons for participants

[MrCoder]

Icons are used in sequence diagrams to represent certain elements (e.g. Actor) or to add notes for clarification(e.g. Boundary, or Entity), show that an participant belongs to a type (e.g. Service).

In ZenUML, we use the following syntax to link an icon to a participant:

@IconName participantName

We already support a list of icons. This issue is to add more icons to the support list.

Checklist

• Add the support of icons in the below list
• Create a page to document all supported icons - Add more icons ZenUml/docs#11

They have been split into groups so we don't have to finish all in one release.

Primary participant types

1. Client
2. Server
3. Browser
4. Service
5. Controller
6. API (Application Programming Interface)
7. UI (User Interface)
8. Mobile
9. ExternalSystem

Secondary participant types

1. Application
2. LoadBalancer
3. Network
4. Cache
5. WebServer
6. MessageQueue
7. Scheduler
8. Gateway
9. AuthenticationService
10. MailServer

Common applications and services

1. GitHub
2. Docker
3. GitLab
4. Jenkins
5. PostgreSQL
6. MongoDB
7. Kubernetes
8. Apache Kafka
9. Elasticsearch
10. Auth0
11. Redis

[MrCoder]

Feel free to create sub tasks for a subset of the icons. Use [sub] in the title and link back to this issue if you are going to create sub tasks.