fix: warehouse stringmap configs are lower case w.r.t viper

[achettyiitr]

Description

• Since viper internally stores its keys in lowercase, we need to compare checking with lowercase for StringMap

Notion Ticket

https://www.notion.so/rudderstacks/warehouse-config-string-map-comparision-in-lower-case-941eae92d77946fc9f41be8d17e5f685?pvs=4

Security

• The code changed/added as part of this pull request won't create any security issues with how the software is being used.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.29 ⚠️

Comparison is base (a8abd1d) 68.31% compared to head (ab3762b) 68.03%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3592      +/-   ##
==========================================
- Coverage   68.31%   68.03%   -0.29%     
==========================================
  Files         318      318              
  Lines       50284    50280       -4     
==========================================
- Hits        34353    34207     -146     
- Misses      13699    13846     +147     
+ Partials     2232     2227       -5     

Impacted Files	Coverage Δ
warehouse/internal/loadfiles/loadfiles.go	75.43% <0.00%> (ø)
warehouse/upload.go	64.69% <0.00%> (-9.66%)	⬇️

... and 8 files with indirect coverage changes

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