Inject identity server token for 3pid invites on createRoom
Inject identity server token for 3pid invites on createRoom

We only inject if needed to avoid potentially overwriting the value with something unknown. The docs in the react-sdk imply this was supposed to happen.

Fixes https://github.com/vector-im/element-web/issues/14814
matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk,matrix-org/matrix-js-sdk