Add: SVN

[ryancheley]

Added SVN as an on premises option for version control

[gabriel-tessier]

@ryancheley

Thanks for the PR but the icon you add have a green background and it don't render well.
Here an icon which is I think more close to the original one (check the favicon) https://subversion.apache.org/

Here how it render I put both and the others vcs icons which may help to compare the render.

And the code to generate the diagrams.

from diagrams import Diagram, Cluster
from diagrams.custom import Custom
from diagrams.onprem.vcs import Git, Github, Gitlab
from urllib.request import urlretrieve


with Diagram("Version control", show=False, filename="version_control", direction="LR"):

    # download the icon image file    
    subversion_url = "https://github.com/mingrammer/diagrams/raw/08817b6ae436dfd0ecdff87a0c32ff7b87560221/resources/onprem/vcs/svn.png"
    subversion_icon = "subversion.png"
    urlretrieve(subversion_url, subversion_icon)
    

    with Cluster("OnPrem"):
        with Cluster("VCS"):
            subversion = Custom("SubVersion", "my_resources/subversion.png")
            subversion_green = Custom("SubVersion", subversion_icon)
            git = Git("Git")
            github = Github("GitHub")
            gitlab = Gitlab("GitLab")

[ryancheley]

@gabriel-tessier thanks (and sorry about that!) I'll update and resubmit my PR

[gabriel-tessier]

Thanks for the icon!
I hope it will be merged soon.

[mingrammer]

Sorry for the late. Thank you.