chore: meaningful name for receivers

[achettyiitr]

Description

• Use a more meaningful name for the receivers present in warehouse/internal/repo package. Currently, we are using repo everywhere. Also we already have a repo struct present inside the package.
• Some feedback in here

Linear Ticket

• Resolves PIPE-472

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

Attention: 123 lines in your changes are missing coverage. Please review.

Comparison is base (b80d273) 71.53% compared to head (a29fa92) 71.70%.
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4064      +/-   ##
==========================================
+ Coverage   71.53%   71.70%   +0.17%     
==========================================
  Files         373      373              
  Lines       54826    54941     +115     
==========================================
+ Hits        39219    39397     +178     
+ Misses      13272    13207      -65     
- Partials     2335     2337       +2     

Files	Coverage Δ
warehouse/api/http.go	78.94% <100.00%> (ø)
warehouse/app.go	89.59% <100.00%> (ø)
warehouse/integrations/testhelper/setup.go	99.68% <100.00%> (ø)
warehouse/internal/model/upload.go	100.00% <ø> (ø)
warehouse/internal/repo/schema.go	88.88% <100.00%> (ø)
warehouse/internal/repo/staging.go	81.77% <100.00%> (ø)
warehouse/integrations/testhelper/verify.go	89.64% <91.66%> (ø)
warehouse/internal/repo/upload.go	91.01% <98.03%> (ø)
warehouse/internal/model/source.go	91.66% <91.66%> (ø)
warehouse/slave/worker.go	81.74% <76.19%> (-0.88%)	⬇️
... and 4 more

... and 9 files with indirect coverage changes

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