[FEATURE REQUEST] Add option for local docker network

[androidseb25]

Add function to connect locally in the docker network via environment variables (hybrid way with the old version)

What we need in iGotify-Notification-Assistent:

• [ ] GOTIFY_URL as environment variable e.g.: 'http://gotify'
• [ ] SECNTFY_TOKEN as environment variable to send notification to an device (semicolon separated for multiple devices)
• [ ] GOTIFY_CLIENT_TOKEN as environment variable to connect to WebSocket (semicolon separated for multiple devices)
• [ ] ReadMe must be updated with new environment variables, when feature is finished, marked this feature as optional

What we need in iGotify iOS App:

• [ ] an switch in the instance add view for disable the connection to the iGotify Container
• [ ] when switch enable show after connection check the following environment variables for the docker compose file or service file (GOTIFY_URL, SECNTFY_TOKEN, GOTIFY_CLIENT_TOKEN)

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expected release of iGotify-Notification-Assistent v1.2.1.0

• June 2024

expected release of iGotify v1.2.1

• June 2024

related issues:

#56 #44