[lib] Specify messageID in sendTextMessageSpec

Summary:
Testing revealed that I had forgotten to specify this.

Depends on D12828

Test Plan:
I followed the test plan described in this Linear comment. Before this diff, I saw this error, which disappeared afterwards:

Failed processing Olm P2P message: [Invariant Violation: new messageInfos should have serverID]

Reviewers: tomek, kamil, marcin

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D12829