Action should not fail credentials are not provided for ChatClient

[ardacetinkaya]

Related to #5

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[ardacetinkaya]

.github/workflows/summarizePR.yml

• Added a step to check for the presence of the AI_API_KEY secret. If not provided, the action is skipped, avoiding unnecessary execution.

src/Summarize.PR/Program.cs

• Refactored the main program to check for the presence of the APIKey before attempting to create a ChatCompletionsClient.
• Introduced a condition to skip ChatClient operations if the APIKey is missing.
• Enhanced logging to inform whether the API Key or Commit SHA is missing, providing better insights during execution.

[ardacetinkaya]

File: .github/workflows/summarizePR.yml

• Updated Step Name: Changed the name of the step that checks for API keys to include "Action Token" as well.
• Added Token Check: Introduced a new check for the presence of the ACTION_TOKEN secret. If it is not available, the action now skips execution with a message indicating the absence of the Action Token.