Default the Datadog, New Relic and Amplitude MCP hosts to the US region

[Mokshit06]

Summary

Follow-up to #5, which made the regional MCP host a required credential (${DATADOG_DD_MCP_DOMAIN} etc.). Users on the default region shouldn't have to know their MCP hostname before the plugin works, so the five URLs now carry a shell-style default:

datadog, datadog-remote:    https://${DATADOG_DD_MCP_DOMAIN:-mcp.datadoghq.com}/…
newrelic, newrelic-remote:  https://${NEWRELIC_MCP_DOMAIN:-mcp.newrelic.com}/mcp/
amplitude:                  https://${AMPLITUDE_MCP_DOMAIN:-mcp.amplitude.com}/mcp

With a saved credential the host is overridden (e.g. mcp.us3.datadoghq.com, mcp.eu.newrelic.com, mcp.eu.amplitude.com); without one the US host is used and the field shows as optional.

scripts/validate.py now validates only the variable name of a ${NAME:-default} reference (placeholder_name), so defaults pass the credential-name check.

Do not merge before usacognition/devin-webapp#72615 is deployed. Until then the runtime strips/ignores the default and would connect to the literal ${…} host. Note also that the URL change is a declaration change, so existing installs of these plugins created from #5's URL will be replaced by the reconciler (saved domain/keys need re-entering) — #5 merged only recently, so exposure is small.

Release notes

The Datadog, New Relic and Amplitude plugins now connect to the US region by default; set the region variable only if your account is hosted elsewhere.

Link to Devin session: https://staging.itsdev.in/sessions/422e2c28c48b4430af245ea6f267f68a
Open in Devin Desktop: https://staging.itsdev.in/desktop/session/422e2c28c48b4430af245ea6f267f68a?variant=devin-insiders
Requested by: @Mokshit06

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Devin Review

Status	Commit
🟢 Reviewed	67b4f6e

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Original prompt from Mokshit

i just tried installing datadog (api key) plugin at my org level. this org already had the datadog (api key) MCP installed with custom headers values set for auth

then when i installed the plugin, it didnt take adopt the auth and instead created a new mcp installation. why?

this is what the old & new one looks like

also hwo do i change server URL in the new one?
ATTACHMENT:"https://staging.itsdev.in/attachments/03927b31-95f7-4dde-ae65-00a843c95dc2/CleanShot%202026-09-04%20at%2003.49.09.png"
ATTACHMENT:"https://staging.itsdev.in/attachments/4b142bcc-7e82-44fd-be35-c3f9918a7fa4/CleanShot%202026-09-04%20at%2003.49.18%402x.png"

[staging-devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

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