feat: Support self-hosted Sentry via DSN

[aryanjsingh]

Summary

This change updates the Sentry configuration to use a DSN (Data Source Name) instead of separate fields for organization, key, and project. This allows users to configure Central with self-hosted Sentry instances. The Nginx configuration has been updated to parse the DSN to construct the CSP reporting endpoint, and the setup is now more robust when Sentry is not configured.

Changes

• .env.template: Replaced SENTRY_ORG_SUBDOMAIN, SENTRY_KEY, and SENTRY_PROJECT with SENTRY_DSN to support self-hosted Sentry instances, which is the standard way to configure Sentry clients.
• files/nginx/odk.conf.template: Updated the /csp-report location block to use a single SENTRY_CSP_ENDPOINT variable. This variable will be constructed from the SENTRY_DSN in the setup-odk.sh script, allowing for flexible Sentry endpoint configuration.
• files/nginx/setup-odk.sh: Added logic to parse the SENTRY_DSN environment variable to construct the Sentry CSP endpoint URL. Also added a fallback for when SENTRY_DSN is not set, which makes the Nginx configuration robust by replacing the Sentry proxy block with a simple return 204 to gracefully handle CSP reports.
• files/service/config.json.template: Updated the backend service configuration to accept a Sentry dsn instead of separate orgSubdomain, key, and project fields. This aligns with the move to a single DSN for Sentry configuration.

Related Issue

Closes #1489

[brontolosone]

@aryanjsingh, as you closed your PR: are you no longer interested in support for self-hosted sentry? Or are you thinking about some other way to accomplish same?