guide: extract `remote add/modify` details from cmd ref.

[jorgeorpinel]

Currently most of the information about remote storage is in the command reference, mainly under the remote add/modify commands (which have expandable details sections for each supported remote type. We can leave some basics in there (cmd refs should be self-contained), but the details need to be in the User Guide instead. Probably as part of #2856

Some related tickets that could potentially be included in this refactoring:

• keep in mind ref: better prioritize and highlight common remote options #1699
• guide: working with SSH remote storage #3832
• guide: using NFS as a remote storage #103
• ref: clarify about obfuscated remote file structure (same as cache) #1762
• + Cover Sharing Data/Models ? (See [spike] cases: address Sharing Data #3186)

This is may be related to #340, as remote definitions are part of the configuration of DVC. But we probably still want a separate guide for this as the remote storage feature goes beyond configuration.

[daavoo]

During support dutty, I usually see a lot of questions related to setting up credentials for remotes.

Perhaps we could try to have guides like the one for Google Drive (with screenshots, etc.) for other popular remotes? (no stats to support but AWS and Azure appear to be the most commonly asked about)

[jorgeorpinel]

Perhaps we could try to have guides like the one for Google Drive (with screenshots, etc.) for other popular remotes?

That would be quite nice but it takes lots of effort to produce and maintain. That guide was generously contributed (and already updated once), yet is probably already outdated as GCP changes their UI and even API regularly.

We def. want to un-bury this info onto the User Guide, but avoid documenting 3rd-party tools whenever possible. That said pointing out the relevant config fields for each remote type is probably very valuable for users, so they don't have to investigate the entire (huge) spec. on storage provider docs.