[Unreal] Change agones component to subsystem

[GloryOfNight]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug
/kind cleanup
/kind documentation
/kind feature
/kind hotfix
/kind release

What this PR does / Why we need it:

• Refactor agones from using ActorComponent to GameInstanceSubsystem:

  • Subsystem is more suitable for agones. Subsystem exists from GameInstance initialization and will proceed to exist during all server lifetime.
  • Subsystem not being part of actor, which is part of the world, would not be destroyed during level change.
  • Subsystem owns its own timer manager, which also would not be affected by world.
  • Subsystem would be created only for server builds by default. That behavior easily changeable since its just virtual func. ShouldCreateSubsystem().

• Removed final keyword, to allow basing of Subsystem and overriding behavior.

• Added bDisableAutoHealthPing to disable auto call to HealthPing() during init

• Added blueprint readonly flag support for HealthRateSeconds, bDisableAutoHealthPing, bDisableAutoConnect so controlling subsystem calls from BPs would be easier.

• Added static Get() of subsystem, so it would be easily obtained from anywhere you have a context object.

• Space&Tabs mix change to just Tabs

Special notes for your reviewer:

That is something we used internally for some time already and I think people can benefit from that change.
This change would break code that was previously dependent on AgonesComponent.

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