feat: add toBool function for template

[zekth]

Currently Deck parses env variable in templates and renders it only as string, with other types it creates issues like having boolean flags for example. With this PR we can do this:

services:
- name: svc1
  host: mockbin.org
  enabled: ${{ env "DECK_MOCKBIN_ENABLED" | toBool }}

Also i think we might want to do the same for Int / floats in the future

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (bd4f876) 35.54% compared to head (26ceb70) 35.56%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #867      +/-   ##
==========================================
+ Coverage   35.54%   35.56%   +0.01%     
==========================================
  Files          92       92              
  Lines       11264    11267       +3     
==========================================
+ Hits         4004     4007       +3     
  Misses       6867     6867              
  Partials      393      393              

Impacted Files	Coverage Δ
file/readfile.go	83.78% <100.00%> (+0.45%)	⬆️

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