Clarify deprecation messages

[paskal]

It turned out we don't really want to break users configurations, so deprecated values stay with us at least before 2.0 is released.

[codecov]

Codecov Report

Merging #1026 (812e9b3) into master (8d8c6ee) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1026   +/-   ##
=======================================
  Coverage   44.01%   44.01%           
=======================================
  Files         127      127           
  Lines        2906     2906           
  Branches      656      656           
=======================================
  Hits         1279     1279           
  Misses       1615     1615           
  Partials       12       12           

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[coveralls]

Pull Request Test Coverage Report for Build 876130532

• 7 of 12 (58.33%) changed or added relevant lines in 2 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.03%) to 83.662%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
backend/app/main.go	0	2	0.0%
backend/app/cmd/server.go	7	10	70.0%

Files with Coverage Reduction	New Missed Lines	%
backend/app/main.go	1	70.59%

Totals
Change from base Build 875954404:	0.03%
Covered Lines:	5438
Relevant Lines:	6500

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💛 - Coveralls