refactor: move getUserConfig to cli utils

[jkjustjoshing]

Issue

When importing localizeUrl() into Astro components, the build failed because @proload packages were being imported in the same file, and Vite doesn't know how to transpile @proload.

import { localizeUrl } from 'astro-i18next';

Proposal

I'm proposing the following change:

•  import { localizeUrl } from 'astro-i18next/utils';
  

• Updating the build script to output a utils.js from src/utils.ts
• Expose utils.js as astro-i18next/utils from package.json

Discussion

I realize I submitted this PR without a corresponding Issue. I'm happy to make that issue, close this PR, and discuss the best solution there before moving forward with a code implementation.
For my project, I needed this change made today, so I figured I'd also submit it back to the project as a proposal.

[codecov-commenter]

Codecov Report

Base: 98.93% // Head: 99.02% // Increases project coverage by +0.08% 🎉

Coverage data is based on head (ff05865) compared to base (9281d7e).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop      #59      +/-   ##
===========================================
+ Coverage    98.93%   99.02%   +0.08%     
===========================================
  Files            4        4              
  Lines          377      409      +32     
  Branches        47       47              
===========================================
+ Hits           373      405      +32     
  Misses           4        4              

Impacted Files	Coverage Δ
src/utils.ts	100.00% <ø> (ø)
src/cli/utils.ts	100.00% <100.00%> (ø)

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[jkjustjoshing]

I've realized my issue is that I'm not actually importing this file into an Astro component, I'm importing this file into a React component that is being pulled in with client:load. So the solution to this will be the same as #46 - the client needs access to the i18next instance