Add ability to skip cleaning the output directory

[tylermmorton]

I've run into a snag recently while using Jet's postgres generator. It completely cleans the output directory when it goes to process code generation on a database schema.

The way that my project is set up, I want to generate multiple schemas into the same directory while also having each schema be in its own subpackage:

   /storage
     /schema
       /public
       /computed
       /telemetry

Unfortunately I can't do this when I call ProcessDB multiple times, because it ends up clearing the /schema folder of the files it just generated.

I tried my best to make the proposed changes backwards compatible but I'm open to feedback. I'll maintain a fork of jet for now but I'd love to see this feature merged.

Thanks

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 40 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.95%. Comparing base (afc4cee) to head (fc748e9).

Files with missing lines	Patch %	Lines
generator/postgres/postgres_generator.go	0.00%	30 Missing ⚠️
generator/template/process.go	33.33%	8 Missing and 2 partials ⚠️

❌ Your patch check has failed because the patch coverage (11.11%) is below the target coverage (90.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #520      +/-   ##
==========================================
- Coverage   91.35%   90.95%   -0.41%     
==========================================
  Files         136      136              
  Lines        8340     8380      +40     
==========================================
+ Hits         7619     7622       +3     
- Misses        545      581      +36     
- Partials      176      177       +1     

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[go-jet]

because it ends up clearing the /schema folder of the files it just generated.

This shouldn't be the case. If you regenerate public schema computed and telemetry should remain intact.

How are you invoking the generator?