Client: Update posting to new v2 endpoint

[enddynayn]

Description
Update submitting a broadcast message using the new v2/content endpoint.

Note this is blocked by

• https://github.com/orgs/AmplicaLabs/projects/12/views/1?pane=issue&itemId=57878890
• https://github.com/orgs/AmplicaLabs/projects/12/views/1?pane=issue&itemId=57880917

Acceptance Criteria

• Update uploading assets to v2/assets
• Posting a message to v2/content
• Ensure the app continues without any breaking changes.

Architecture