Change default room version to 11. implments MSC4239

[ShadowRZ]

Closes: #18530

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[reivilibre]

Part of #18531

[reivilibre]

looks like this breaks a few tests, sadly; those will need sorting out before merging

[ShadowRZ]

SyTest and Complement also needs to be updated to account for the lack of creator field in m.room.create event in v11 rooms.

[anoadragon453]

SyTest and Complement also needs to be updated to account for the lack of creator field in m.room.create event in v11 rooms.

@ShadowRZ are you able to create PRs for Sytest and Complement to address that? Or would you prefer someone else take that on?