Fix welcome message not showing when joining a room

Fix welcome message not showing when joining a room

Fix https://gitlab.com/gitlab-org/gitter/webapp/issues/2368

Restores passing in embedded to contextGenerator.generateTroupeContext, as we did in https://gitlab.com/gitlab-org/gitter/webapp/commit/c2a4e7dde5124960745b563de3f909607a7db36d#2bdd6ace9e9f516349e8aca5e1a4b77bbecc6950_112_111 (this was removed in https://gitlab.com/gitlab-org/gitter/webapp/commit/685df019a90afe5d8bb6d1c44fc398c6507ca1be#2bdd6ace9e9f516349e8aca5e1a4b77bbecc6950_117_115)

Testing strategy

1. Create a room with a welcome message
2. Leave the room and press the "Join Room" button
3. Notice the welcome message

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1. Visit the same room but the embed view like how Sidecar uses, http://localhost:5000/<community>/<room>/~embed
2. Press "Join Room"
3. Notice how you join the room without a welcome message