bug: not all regions support m6a instance type used by batch job

[Rob-Powell]

As reported in this issue: https://github.com/aws-samples/aws-genai-llm-chatbot/issues/483

M6A is not supported in Paris region as set in the code here:

https://github.com/aws-samples/aws-genai-llm-chatbot/blob/main/lib/rag-engines/data-import/file-import-batch-job.ts#L41 https://github.com/aws-samples/aws-genai-llm-chatbot/blob/main/lib/rag-engines/data-import/web-crawler-batch-job.ts#L41

Need to select an alternate type more widely available or select it dynamically.