docs(edge): Add @clayms examples

[gabriel-tessier]

I added @clayms examples as he is certainly busy and didn't push any PR so far, except if I mess it.

@mingrammer
I mainly copy paste what @clayms wrote in the issues, maybe it's better that he review as he authored the code, I tested and generated the png files so the code is correct but maybe there's some missing comments.
Original discussion started here:
#433

Also in the bellow issue he listed a lot of examples but I'm not sure that it will help to add it in the doc as it's more related to graphviz attributes that Diagrams only use. Sorry if I'm not clear but what I want to say is if graphviz make some breaking changes with this attributes it will broke Diagrams and Diagrams can't do anything about.
WDYT?

[clayms]

Thanks @gabriel-tessier

Knowing what I now know, for the first example I would change the Custom class node to simply a Node class node so the end user would not have to create their own "transparent.png" file. I would then set the Node width and height to "0" so the Edges carried straight through uninterrupted.

Then only change the text to reflect that.

Also replace the word "slave."

I have made some other minor edits to the text inline.

Full code below.

from diagrams import Cluster, Diagram, Edge, Node
from diagrams.onprem.analytics import Spark
from diagrams.onprem.compute import Server
from diagrams.onprem.database import PostgreSQL
from diagrams.onprem.inmemory import Redis
from diagrams.onprem.aggregator import Fluentd
from diagrams.onprem.monitoring import Grafana, Prometheus
from diagrams.onprem.network import Nginx
from diagrams.onprem.queue import Kafka


with Diagram("\nAdvanced Web Service with On-Premise Less edges", show=False):
    ingress = Nginx("ingress")

    with Cluster("Service Cluster"):
            serv1 = Server("grpc1")
            serv2 = Server("grpc2")
            serv3 = Server("grpc3")

    with Cluster(""):
        blankHA = Node("", shape="plaintext", width="0", height="0")
        
        metrics = Prometheus("metric")
        metrics << Grafana("monitoring")
        
        aggregator = Fluentd("logging")
        blankHA >> aggregator >> Kafka("stream") >> Spark("analytics")
        
        with Cluster("Database HA"):
            master = PostgreSQL("users")
            master - PostgreSQL("replica") << metrics
            blankHA >> master
        
        with Cluster("Sessions HA"):
            master = Redis("session")
            master - Redis("replica") << metrics
            blankHA >> master

    ingress >> serv2 >> blankHA

[clayms]

bulk of code is in a comment to the whole PR.

[gabriel-tessier]

I think I didn't mess up too much and applied all your requested changes without mistakes.
I thought I can apply the comment you made in the review but somehow I couldn't. So I copy paste and commit again, I only hope that I forget nothing.
I also re-generate the 2 diagrams png files.

Thanks again for the review.

[tvqphuoc01]

@gabriel-tessier seem like we have some conflict here.

[gabriel-tessier]

@tvqphuoc01

conflict solved