Add src-link generator

[onmax]

This PR introduces a new generator called src-link for AutoMD. The generator allows users to create Markdown links to specific lines in source code files:

Examples:

GitHub URLs

<!-- automd:src-link url="gh:nuxt/nuxt/blob/main/packages/schema/src/types/hooks.ts" pattern="export interface NuxtHooks {" label="schema source code" -->
<!-- /automd -->

Will produce:

[schema source code](https://github.com/nuxt/nuxt/blob/main/packages/schema/src/types/hooks.ts#L83)

GitHub URLs with Regex

<!-- automd:src-link url="gh:nuxt/nuxt/blob/main/packages/schema/src/types/hooks.ts" pattern="Kit[^}]*'kit:compatibility" label="Kit compatibility" -->
<!-- /automd -->

Will produce:

[Kit compatibility](https://github.com/nuxt/nuxt/blob/main/packages/schema/src/types/hooks.ts#L84-L91)

Relative URLs

<!-- automd:src-link url="./types/hooks.ts" pattern="export interface NuxtHooks {" label="schema source code" -->
<!-- /automd -->

Will produce:

[schema source code](./types/hooks.ts:83)

Check the test cases to see more options.

Related #77

[pi0]

Can you please extend existing tests? 🙏🏼

https://github.com/unjs/automd/tree/main/test/fixture

[codecov]

Codecov Report

Attention: Patch coverage is 95.14563% with 5 lines in your changes missing coverage. Please review.

Please upload report for BASE (main@ae3ca7a). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
src/generators/src-link.ts	95.04%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #78   +/-   ##
=======================================
  Coverage        ?   77.55%           
=======================================
  Files           ?       18           
  Lines           ?     1114           
  Branches        ?      158           
=======================================
  Hits            ?      864           
  Misses          ?      249           
  Partials        ?        1           

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[onmax]

Not sure how to register the generator in the config/automd