BossRoom editor update to 6000.3 LTS

[michalChrobot]

Description

This PR updates the editor version on the default branch to 6000.3.20f1 in order to keep up with Playtests (as otherwise I can get build failures related to packages that I cannot remove for 6000.0 but I need to remove for 6000.3)

Some other changes include:

1. Update of NGO to latest 2.13.1 version. This is more of a nitpick since we always test with latest changes but we can definetly confirm that this NGO version works with BossRoom so I think it's nice to bump it
2. Update of tools package to 2.2.9. This is also more of a nitpick for latest bug fixes
3. Update of com.unity.services.multiplayer to 2.2.4 since it resolves issues around NetworkManager usage
4. Update of com.unity.transport to 2.7.4 since it resolves issues around MTU discovery and for example VPN usage that we were encountering in our playtests

I also saw that we were getting a warning warning NETSDK1138: The target framework 'net6.0' is out of support and will not receive security updates in the future so I went and updated the version to 8.0

I Playtested with those modifications and everything works as expected. Changes are focused around helping in our NGO Playtesting

Note that 6000.0 compatible version will still be available on project-version/6000.0 branch

[unity-cla-assistant]

All committers have signed the CLA.

[NoelStephensUnity]

🚀

[EmandM]

Looks sensible to me as long as the checks are passing.

[michalChrobot]

quick comment that I'm not sure how Packages/com.unity.multiplayer.samples.coop should be handled as I can see in the changelog that 3.0.0 (pic1) was released while internally this version is still 2.0.0 (pic2).

Basd on this I'm not sure if my changes (changing the default editor to 6000.3 on the default branch) should constitute any change here