remote: credentials: raise error when credentials don't exist

[boscacci]

Bug Report

push: fails ambiguously when your credentialpath is incorrectly set

Description

I spent a long time spinning my wheels trying to figure out why I couldn't push to remote storage. The clearest error messaging I could get was like this, from verbose output:

File "/opt/homebrew/Cellar/python@3.10/3.10.6_2/Frameworks/Python.framework/Versions/3.10/lib/python3.10/asyncio/selector_events.py", line 500, in sock_connect
    return await fut
asyncio.exceptions.CancelledError

and

ERROR: unexpected error - Connect timeout on endpoint URL: "http://169.254.169.254/latest/api/token"

Ultimately, I figured out that this was happening just because I had the credentialpath incorrectly set in my .dvc/config file. I wish DVC would have told me that the path listed there did not exist!

Reproduce

1. Configure a DVC repo with remote storage (e.g. S3) credentialed via .dvc/config
2. Within .dvc/config purposely set credentialpath = {some_filepath_that_does_not_exist}
3. Try running dvc push. This should result in the same Connect timeout on endpoint URL error I got

Expected

Un-helpful error output:

ERROR: unexpected error - Connect timeout on endpoint URL: "http://169.254.169.254/latest/api/token"

Environment information

DVC version: 2.27.2 (brew)

Platform: Python 3.10.6 on macOS-12.6-arm64-arm-64bit
Subprojects:
dvc_data = 0.10.0
dvc_objects = 0.4.0
dvc_render = 0.0.11
dvc_task = 0.1.2
dvclive = 0.10.0
scmrepo = 0.1.1
Supports:
azure (adlfs = 2022.9.1, knack = 0.10.0, azure-identity = 1.11.0),
gdrive (pydrive2 = 1.14.0),
gs (gcsfs = 2022.8.2),
http (aiohttp = 3.8.1, aiohttp-retry = 2.8.3),
https (aiohttp = 3.8.1, aiohttp-retry = 2.8.3),
oss (ossfs = 2021.8.0),
s3 (s3fs = 2022.8.2, boto3 = 1.24.59),
ssh (sshfs = 2022.6.0),
webdav (webdav4 = 0.9.7),
webdavs (webdav4 = 0.9.7),
webhdfs (fsspec = 2022.8.2)
Cache types: reflink, hardlink, symlink
Cache directory: apfs on /dev/disk3s1s1
Caches: local
Remotes: s3
Workspace directory: apfs on /dev/disk3s1s1
Repo: dvc, git

Additional Information (if any):