Add --allow-custom-scopes flag to skip scope validation.

[Haard30]

This PR adds a --allow-custom-scopes flag to skip scope validation for PAT. This allows addition undocumented ADO scopes.

Testing:

1. PAT with just 1 invalid scope.
   Earlier
   

With --allow-custom-scopes flag

microsoft-authentication-cli\dist on  user/haashah/add-no-validate-flag [!]
❯ .\azureauth.exe ado pat  --organization "office" --scope "lolwut" --display-name "Test PAT" --prompt-hint "Creating custom PAT test" --allow-custom-scopes
Skipping scopes validation.
<pat>

2. PAT with 1 known and 1 invalid scope

❯ .\azureauth.exe ado pat  --organization "office" --scope "lolwut" --scope "vso.code" --display-name "Test PAT 2" --prompt-hint "Creating PAT for testing" --allow-custom-scopes
Skipping scopes validation.
One or more errors occurred. (Failed to create PAT: InvalidScope)
An unexpected error ocurred. Re-run with --verbosity=debug for more info.

3. PAT with valid known ADO scope and valid unknown ADO scope.

❯ .\azureauth.exe ado pat  --organization "office" --scope "vso.governance" --scope "vso.code" --display-name "Non-public valid scope" --prompt-hint "Creating PAT for testing" --allow-custom-scopes
Skipping scopes validation.
<pat>

4. Without --allow-custom-scopes flag

❯  .\azureauth.exe ado pat  --organization "office" --scope "vso.governance" --scope "vso.code" --display-name "Non-public valid scope" --prompt-hint "Creating PAT for testing"
vso.governance is not a known Azure DevOps PAT scope.
Consult https://aka.ms/azure-devops-pat-scopes for a list of known scopes.
Use --allow-custom-scopes to create a PAT with custom scopes.

[reillysiemens]

Consider renaming this option to --allow-custom-scopes as that might be a little bit more self-explanatory.