Parse operation configs only if they are specified

[Algebro7]

This fixes a bug where duplicacy-util tries to parse configurations for all operations, even when they aren't specified. Now each configuration is only parsed when the corresponding cmd* flag is passed. It does not change any behavior for the end user.

performBackup() in backup-ops.go correctly honors these flags already, so not parsing the configs should not break anything.

[Algebro7]

Looks like the config unit tests need some additional work since these flags aren't passed there

[Algebro7]

Updated the unit tests to set the required flags, but do they need to be outside the function so that they are guaranteed to be available everywhere? I'm not sure how golang's testing works as far as threading and such.

[codecov]

Codecov Report

Merging #52 into master will decrease coverage by 0.06%.
The diff coverage is 51.11%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   40.36%   40.29%   -0.07%     
==========================================
  Files          12       12              
  Lines         934      938       +4     
==========================================
+ Hits          377      378       +1     
- Misses        515      517       +2     
- Partials       42       43       +1     

Impacted Files	Coverage Δ
configBackup.go	51.79% <51.11%> (+1.42%)	⬆️
timeutils.go	79.03% <0.00%> (-4.84%)	⬇️

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