Support ODT/OpenDocument Text document extraction

### Self Checks - [x] I have read the [Contributing Guide](https://github.com/langgenius/dify/blob/main/CONTRIBUTING.md) and [Language Policy](https://github.com/langgenius/dify/issues/1542). - [x] I have searched for existing issues [search for existing issues](https://github.com/langgenius/dify/issues), including closed ones. - [x] I confirm that I am using English to submit this report, otherwise it will be closed. - [x] Please do not modify this template :) and fill in all the required fields. ### 1. Is this request related to a challenge you're experiencing? Tell me about your story. Dify currently supports many document formats for knowledge ingestion and workflow document extraction, but OpenDocument Text files (`.odt`) are not included in the document extension allowlist. This makes it impossible to upload or route `.odt` files through the same extraction path as other office document formats, even though `.odt` is a common open standard format used by LibreOffice, OpenOffice, and other document editors. The upstream `langgenius/graphon` package already added OpenDocument Text extraction support in `langgenius/graphon#203`, and that support is available in Graphon `v0.7.0`. Dify `main` is already pinned to `graphon==0.7.0`, so the remaining Dify-side work is to expose `.odt` in the document extension allowlist and cover the document extractor routing behavior. Proposed behavior: - Allow `.odt` in Dify document extension allowlists for both SelfHosted and Unstructured ETL modes. - Route `.odt` files to the Graphon OpenDocument Text extractor. - Route `application/vnd.oasis.opendocument.text` MIME type to the same extractor path. - Add regression tests for constants and document extractor routing. I opened an initial implementation PR at https://github.com/langgenius/dify/pull/39973, but it was closed because this feature request had not been discussed in an associated issue first. Opening this issue to discuss the change before reopening or recreating the PR. ### 2. Additional context or comments Relevant upstream and implementation references: - Graphon ODT support PR: https://github.com/langgenius/graphon/pull/203 - Graphon release containing ODT support: https://github.com/langgenius/graphon/releases/tag/v0.7.0 - Initial Dify implementation PR: https://github.com/langgenius/dify/pull/39973 The initial PR included: - adding `odt` to Dify document extension lists - tests for SelfHosted and Unstructured ETL document extensions - tests for `.odt` extension and `application/vnd.oasis.opendocument.text` MIME routing through the document extractor Local validation from the initial PR: - targeted ODT tests passed - `make lint` passed - targeted type-check for changed files passed - `TZ=UTC make test` passed ### 3. Can you help us with this feature? - [x] I am interested in contributing to this feature.