ref(migrations): ddl timeout 5min -> 20min

[MeredithAnya]

No description provided.

[sentry]

Bug: The server-side DDL timeout (10 min) is longer than the client-side HTTP timeout (5 min), creating a risk of premature client timeouts during long migrations.
_{Severity: MEDIUM}

Suggested Fix

To ensure consistency and prevent potential timeout failures, increase the client-side send_receive_timeout in the MIGRATE profile to match the server-side distributed_ddl_task_timeout. Set it to at least 600000 milliseconds (10 minutes).

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: snuba/clusters/cluster.py#L65-L68

Potential issue: The pull request increases the server-side
`distributed_ddl_task_timeout` to 600 seconds (10 minutes) but leaves the corresponding
client-side HTTP `send_receive_timeout` for the `MIGRATE` profile at 300 seconds (5
minutes). While the use of `send_progress_in_http_headers` is intended to keep the
connection alive, this timeout mismatch creates a latent bug. If for any reason (e.g., a
bug in ClickHouse, a network issue, or a misconfiguration) the progress headers are not
sent for a 5-minute interval, a long-running migration (between 5 and 10 minutes) will
fail due to a client-side timeout, even though the server is configured to allow it to
complete.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[phacops]

I think I'd rather do #8416 than just increase the timeout.