new feature: publish Python bindings to Anaconda Defaults

## Feature Description

Publish the OpenDAL Python binding as a Conda package in Anaconda Defaults (`main`) so users can install it with:

```console
conda install main::opendal
```

This should cover the platforms supported by the Python binding and the Python versions supported by its released package metadata.

## Problem and Solution

The Python binding is available on PyPI, but `opendal` is currently absent from Anaconda Defaults. This also blocks `opendalfs` from being published to `main`, because `opendalfs` has a runtime dependency on `opendal` and a clean Conda environment cannot resolve that dependency today.

A practical path is:

1. Complete the conda-forge packaging tracked by #4391.
2. Request adoption of the resulting feedstock into Anaconda Defaults, following the process documented by [AnacondaRecipes/aggregate](https://github.com/AnacondaRecipes/aggregate#how-to-add-new-recipes-to-the-aggregate-repository) or the current Anaconda package-request process.
3. Verify the package from a clean environment on each supported Defaults platform.
4. Document ownership and automate version updates for future OpenDAL Python releases.

Acceptance criteria:

- [ ] A maintained Conda recipe/feedstock builds the released Python binding from source with matching Python support and runtime metadata.
- [ ] Packages are available from Anaconda Defaults for the supported platform set, including `linux-64`, `linux-aarch64`, `osx-64`, `osx-arm64`, and `win-64` where the dependency set supports them.
- [ ] `conda install main::opendal` succeeds in a clean environment.
- [ ] `python -c "import opendal"` succeeds after installation.
- [ ] The feedstock has documented maintainers and an update path for future tagged releases.

## Additional Context

- Existing conda-forge request: #4391
- Downstream request blocked on this package: https://github.com/fsspec/opendalfs/issues/61
- Current `opendalfs` requirement: `opendal>=0.47.5,<0.48`