feat: support alias_attribute as valid keys for filter

[brunohkbx]

Summary

Given a model with an alias_attribute like so:
alias_attribute :title_alias, :title

Then it will be possible to use the alias as a valid filter:
filter :title_alias, as: :select

[javierjulio]

Does this work with other filter types? What if using a Ransack based filter? This just needs a rebase and push to run CI. Thank you.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (0a1521d) 99.47% compared to head (00e298b) 99.47%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6956   +/-   ##
=======================================
  Coverage   99.47%   99.47%           
=======================================
  Files         308      308           
  Lines       11306    11321   +15     
=======================================
+ Hits        11247    11262   +15     
  Misses         59       59           

Impacted Files	Coverage Δ
lib/active_admin/filters/formtastic_addons.rb	96.77% <100.00%> (+0.34%)	⬆️
lib/active_admin/inputs/filters/select_input.rb	100.00% <100.00%> (ø)
spec/unit/filters/filter_form_builder_spec.rb	99.41% <100.00%> (+0.01%)	⬆️

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