feat: implement permission validation for Slack slash commands#75

nuel-solutions wants to merge 2 commits intoaws-samples:v4/slack-integrationaws-samples/sample-aws-security-incident-response-integrations:v4/slack-integrationfrom

nuel-solutions:v4/slack-permission-validationnuel-solutions/sample-aws-security-incident-response-integrations:v4/slack-permission-validationCopy head branch name to clipboard