arrow

GH-40036: [C++] Azure file system write buffering & async writes (#43096)

### Rationale for this change

See #40036.

### What changes are included in this PR?

Write buffering and async writes (similar to what the S3 file system does) in the `ObjectAppendStream` for the Azure file system.

With write buffering and async writes, the input scenario creation runtime in the tests (which uses the `ObjectAppendStream` against Azurite) decreased from ~25s (see [here](https://github.com/apache/arrow/issues/40036)) to ~800ms:
```
[ RUN      ] TestAzuriteFileSystem.OpenInputFileMixedReadVsReadAt
[       OK ] TestAzuriteFileSystem.OpenInputFileMixedReadVsReadAt (787 ms)
```

### Are these changes tested?
Added some tests with background writes enabled and disabled (some were taken from the S3 tests). Everything changed should be covered.

### Are there any user-facing changes?
`AzureOptions` now allows for `background_writes` to be set (default: true). No breaking changes.

### Notes

- The code in `DoWrite` is very similar to [the code in the S3 FS](https://github.com/apache/arrow/blob/edfa343eeca008513f0300924380e1b187cc976b/cpp/src/arrow/filesystem/s3fs.cc#L1753). Maybe this could be unified? I didn't see this in the scope of the PR though.
* GitHub Issue: #40036

Lead-authored-by: Oliver Layer <o.layer@celonis.de>
Co-authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>