Fix variants setup for Android

[arthurpalves]

What does this PR do

• Decodes android.signing as optional
• Writes fastlane/ in the base folder regardless of the path in android.path
• Throws RuntimeError with more descriptive error message when writing to fastlane parameter files
• Removes redundant ❌ when instantiating RuntimeError

How can it be tested

• Generate new spec with variants init
• Replace the following placeholders with correct value:
  • android.path
  • android.app_name
  • android.app_identifier
• Run variants setup

Checklist:

• I ran make validation locally with success
• I have not introduced new bugs
• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new errors

[backbaseoss]

	Warnings
⚠️	The library files were changed, but the tests remained unmodified. Consider updating or adding to the tests to match the library changes.

Generated by 🚫 Danger Swift against 7679f6d

[codecov]

Codecov Report

Merging #133 (e04b1a7) into develop (f4b59be) will decrease coverage by 0.10%.
The diff coverage is 45.45%.

@@             Coverage Diff             @@
##           develop     #133      +/-   ##
===========================================
- Coverage    62.90%   62.79%   -0.11%     
===========================================
  Files           31       31              
  Lines         1170     1172       +2     
===========================================
  Hits           736      736              
- Misses         434      436       +2     

Impacted Files	Coverage Δ
.../VariantsCore/Custom Types/TemplateDirectory.swift	60.00% <0.00%> (ø)
...ces/VariantsCore/Custom Types/UtilsDirectory.swift	60.00% <0.00%> (ø)
...riantsCore/Factory/FastlaneParametersFactory.swift	28.37% <0.00%> (ø)
...antsCore/Custom Types/Project/AndroidProject.swift	85.58% <66.66%> (-1.58%)	⬇️
...ntsCore/Schemas/Android/AndroidConfiguration.swift	100.00% <100.00%> (ø)

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