[i18n] Update CNCF maturity status in all locale homepages

Update localized homepages that still describe OpenTelemetry as a CNCF incubating project. Match `content/en/_index.md`: OpenTelemetry is now a CNCF graduated project. | Locale | File | Approvers | |---|---|---| | Bengali | `content/bn/_index.md` | @open-telemetry/docs-bn-approvers | | French | `content/fr/_index.md` | @open-telemetry/docs-fr-approvers | | Polish | `content/pl/_index.md` | @open-telemetry/docs-pl-approvers | | Romanian | `content/ro/_index.md` | @open-telemetry/docs-ro-approvers | When patching each page, add `# patched` at the end of its `default_lang_commit` front matter line. ### Name + path of the page `content/{bn,fr,pl,ro}/_index. localized homepagesmd` ### Additional context The English homepage was updated in #9873. `content/zh/_index.md` already says graduated, so it is not included. For unstaffed locale fallback ownership, cc @open-telemetry/docs-approvers. ### Scope Note to locale team: this is a patch update, you don't have to make a full homepage alignment update, just patch the CNCF maturity status.