Add optional directory input to GitHub action

[Sherlouk]

Justification

I understand that this is not the most common use case, but some teams use a mono-repo where the Package.swift may not be at the root of the project. In my project, I have multiple directories containing multiple Swift Vapor servers. Unfortunately this GitHub action in its current form would not work as it was unable to run the Swift command from the root of the project.

Changes

This pull request introduces a new input parameter called "directory". If provided, this will change the active directory to the path provided before running any further commands.

    - name: Check Swift Package dependencies
      id: spm-dep-check
      uses: Sherlouk/swift-package-dependencies-check@main
      with:
         isMutating: true
         failWhenOutdated: false
         directory: 'Ingest'

It has been tested with the above snippet, it successfully found the "Ingest" directory. This is not a breaking change.

Apology

I made all the code changes within GitHub's file editor which is not the great but is my excuse for the poor commits. Feel free to squash/rebase into a single commit.

[MarcoEidinger]

Hi @Sherlouk, great idea and wonderful that you opened this pull request !! Will merge it soon. Once merged I will create version 2.1.3 and switch v2 to it

[MarcoEidinger]

Merged, version 2.1.3 created and v2 switched :)

Thank you again @Sherlouk and I mentioned you on Twitter to express my gratitude

https://twitter.com/MarcoEidinger/status/1493466000410365953