Better error messages for objectsack swift configuration

[icewind1991]

try to figure out specificly what's wrong with the config and try to give suggestions how to fix it instead of just throwing generic exceptions.

[mention-bot]

@icewind1991, thanks for your PR! By analyzing the history of the files in this pull request, we identified @butonic, @nickvergessen and @MorrisJobke to be potential reviewers.

[oparoz]

Great! 👍

[codecov-io]

Codecov Report

Merging #4112 into master will decrease coverage by 0.02%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##             master   #4112      +/-   ##
===========================================
- Coverage     54.23%   54.2%   -0.03%     
- Complexity    21278   21294      +16     
===========================================
  Files          1310    1310              
  Lines         81213   81253      +40     
  Branches       1285    1285              
===========================================
+ Hits          44043   44045       +2     
- Misses        37170   37208      +38

Impacted Files	Coverage Δ	Complexity Δ
lib/private/Files/ObjectStore/Swift.php	0% <0%> (ø)	33 <9> (+16)	⬆️
lib/private/Files/Cache/Propagator.php	94.93% <0%> (-1.27%)	16% <0%> (ø)
apps/files_trashbin/lib/Trashbin.php	73.64% <0%> (+0.24%)	133% <0%> (ø)	⬇️
apps/comments/lib/EventHandler.php	87.5% <0%> (+8.33%)	7% <0%> (ø)	⬇️

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[MorrisJobke]

Tested and works 👍