show correct error and keep modal open

[mslourens]

Description

When the connection to a data source fails, a very generic error is thrown and the modal is closed. This should not happen, the user should be able to fix the issue and know what's wrong. This PR fixes #4812

Screenshots

[codecov-commenter]

Codecov Report

Merging #4838 (4df23dd) into develop (86f649c) will decrease coverage by 0.05%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #4838      +/-   ##
===========================================
- Coverage    69.51%   69.45%   -0.06%     
===========================================
  Files          145      145              
  Lines         4979     4983       +4     
  Branches       765      766       +1     
===========================================
  Hits          3461     3461              
- Misses        1066     1069       +3     
- Partials       452      453       +1     

Impacted Files	Coverage Δ
...kages/server/src/api/controllers/table/external.js	7.97% <0.00%> (-0.24%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 946d245...4df23dd. Read the comment docs.

[shogunpurple]

Nice fix here! Thanks @mslourens