Document how to acquire OneDrive's access_token or at least refer to useful information

[simonsan]

Relevant information from openDAL side:

Cross-posting relevant replies from imWildCat #2129 (comment)

To get a working access_token for OneDrive, we can leverage https://crates.io/crates/graph-rs-sdk, especially its demo: https://github.com/sreeise/graph-rs-sdk/tree/master/examples/oauth

From #2129 (comment)

If you'd like to check some tutorials, I did find a quick for you: https://www.youtube.com/watch?v=NljQx11YqNY
In general, OAuth flows for these big techs are pretty complex, sometimes replying on their own SDKs by default. I was working in MSFT. So I knew this very well. For example, if you'd like to use Graph API on iOS/macOS, you might want https://github.com/AzureAD/azure-activedirectory-library-for-objc Why this flow is always complicated? Because they must respect users' privacy and also data compliance, like GDPR. So it is always required something like "User Consent".
The goal of OpenDAL is just a light-weight wrapper of some data uploading / downloading apis. So this lib is not depending on any of these first-party SDKs provided by the service companies.
In my own company, I write these logic into Rust directly, referring to the sample code link I shared above. You'd better check them out before being surprised here. This flow would be easier for you if you write them in Rust for all the other big ones, like Google and/or Dropbox.

Ref: #1161 apache/opendal#4715

[intgr]

FWIW the current Rustic release 0.7.0 has OpenDAL OneDrive support disabled too, so documentation is misleading. I had to manually edit Cargo.toml and rebuild to enable it.

Ref: #1161 (comment)

[simonsan]

@intgr Would you be able to provide some information about the onedrive config you are using and pull request it against this directory: https://github.com/rustic-rs/rustic/tree/main/config/services

Would be a nice addition :)