Description of problem:
dnf / yum produces Error: Failed to synchronize cache for repo 'rhel'
even if there is a typo in yum.repos.d file or the url doesn't exist.
This error is most cases misleading. It mentions cache, users will be looking for problems with cache, while most usual cause of this error is typo in config or issue with network connection. 

Version-Release number of selected component (if applicable):
yum-4.0.9.2-5.el8.noarch

How reproducible:
always 

Steps to Reproduce:
1. vim /etc/yum.repos.d/rhel.repo
2. update baseurl to non existing or invalid url
3. yum search foo

Actual results:
Error: Failed to synchronize cache for repo 'rhel'

Expected results:
Experiencing this is one of the most common errors, dnf should probably display information to help user solve the problem (like yum did): 

Error parsing config: Error parsing "baseurl = ...": URL must be http, ftp, file or https not "typo"
OR: Could not resolve host (Check network connections)
OR: HTTP Error 404 - Not Found (Check for typo)

Additional info:
Usability issue with high impact
RHEL7 yum parses the repo file for errors, which dnf seem to be not doing
RHEL8  with debugging shows bit more info # dnf -v search foo
Cannot download repodata/repomd.xml: All mirrors were tried.
But this is still not sufficient to quickly identify root cause of the problem and not diplayed in default debug level.