Explicitly document that game servers are only protected from termination in the allocated state

[D3luxee]

This adds documentation that explicitly explains that only allocated game servers are protected from termination and that game servers can be terminated at any time in all other states.

[hloeffler]

While the changes in this PR don't seem to cause any issues, I think there's a larger point of confusion in the documentation that's worth addressing.

The page at https://docs.gamefabric.com/multiplayer-servers/getting-started/using-the-agones-sdk has the heading "Using the Agones SDK". This phrasing makes it sound like using the Agones SDK is optional. However, my understanding is that Agones is a requirement for GameFabric's multiplayer servers.

This could lead to confusion for new users. It might be helpful to update the documentation to make it more explicit that Agones is a necessary component, not just an optional tool."

[D3luxee]

While the changes in this PR don't seem to cause any issues, I think there's a larger point of confusion in the documentation that's worth addressing.

The page at https://docs.gamefabric.com/multiplayer-servers/getting-started/using-the-agones-sdk has the heading "Using the Agones SDK". This phrasing makes it sound like using the Agones SDK is optional. However, my understanding is that Agones is a requirement for GameFabric's multiplayer servers.

This could lead to confusion for new users. It might be helpful to update the documentation to make it more explicit that Agones is a necessary component, not just an optional tool."

After some back and forth in slack this will be addressed in #103