Add configurable API suffix

[sneridagh]

What changed

Adds a configurable API traversal suffix for Volto. This is resolved like we did for @plone/client initialize method, using apiSuffix. In Volto, we go for:

• Introduces config.settings.apiSuffix, with RAZZLE_API_SUFFIX as its environment-variable counterpart.
• Centralizes suffix resolution in getApiSuffix() and uses it across API URL formatting, backend URL expansion, authenticated resource requests, and sitemap requests.
• Keeps existing behavior by default: Volto continues to use /++api++.
• Gives an explicitly configured apiSuffix precedence over legacyTraverse.
• Supports an empty suffix (RAZZLE_API_SUFFIX='' or apiSuffix: '') to intentionally omit traversal.
• Hydrates RAZZLE_API_SUFFIX from window.env so seamless-mode runtime configuration stays consistent between SSR and browser requests.
• Adds a feature Towncrier entry and documents the new environment variable.

Why

Volto currently chooses only between the fixed /++api++ suffix and no suffix through legacyTraverse.
Deployments that expose the Plone API under another traversal suffix need a supported configuration option without relying on the legacy traversal switch.
Deployments for Plone Nick will also need to setup this to empty string.

Impact

Integrators can configure a nonstandard API traversal suffix through config.settings.apiSuffix or RAZZLE_API_SUFFIX.
The setting overrides legacyTraverse when present, while existing installations retain their current behavior when it is absent.

Validation

• pnpm --filter @plone/volto test --run src/helpers/Url/Url.test.js src/helpers/Api/Api.plone.rest.test.js src/helpers/Api/PloneBackendAPIResourceWithAuth.test.js
  • 109 tests passed.
• Prettier check passed for the changed source, type, documentation, and test files.
• Commit hooks passed, including package lint/format checks and the i18n check.
• pnpm --filter @plone/volto check:ts still reports existing unrelated typing errors in widget and Storybook files; no errors are associated with this change.

[read-the-docs-community]

Documentation build overview

📚 volto | 🛠️ Build #33691924 | 📁 Comparing 4996123 against latest (7f1c249)

  🔍 Preview build  

2 files changed

± genindex.html
± configuration/environmentvariables.html

[sneridagh]

Superseded by #8392, which uses the corrected configurable-api-suffix branch name and includes the missing @plone/types Towncrier entry.