Add schema-based rules for package data of package index

[per1234]

These are the JSON schema-based rules to check the root and package level data of package indexes.

[codecov-commenter]

Codecov Report

Merging #194 (a60ecef) into main (ad3f06b) will increase coverage by 0.92%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #194      +/-   ##
==========================================
+ Coverage   84.23%   85.15%   +0.92%     
==========================================
  Files          43       43              
  Lines        3210     3389     +179     
==========================================
+ Hits         2704     2886     +182     
+ Misses        394      392       -2     
+ Partials      112      111       -1     

Flag	Coverage Δ
unit	85.15% <100.00%> (+0.92%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ternal/rule/ruleconfiguration/ruleconfiguration.go	100.00% <ø> (ø)
internal/rule/rulefunction/packageindex.go	89.92% <100.00%> (+18.21%)	⬆️
internal/project/projectdata/packageindex.go	100.00% <0.00%> (+5.55%)	⬆️

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