Update Identity blurbs in readmes

[billwert]

There's a bunch of readmes that still include language like this:

After setup, you can choose which type of [credential][azure_identity_credential_type] from azure.identity to use.
As an example, [DefaultAzureCredential][wiki_identity] can be used to authenticate the client:
Set the values of the client ID, tenant ID, and client secret of the AAD application as environment variables:

This should be updated to not promote a SP at a minimum.

Current list of files:

sdk\textanalytics\azure-ai-textanalytics\README.md
sdk\schemaregistry\azure-data-schemaregistry\README.md
sdk\purview\azure-analytics-purview-scanning\README.md
sdk\purview\azure-analytics-purview-administration\README.md
sdk\openai\azure-ai-openai\README.md
sdk\monitor\azure-monitor-ingestion\README.md
sdk\metricsadvisor\azure-ai-metricsadvisor\README.md
sdk\formrecognizer\azure-ai-formrecognizer\README.md
sdk\documentintelligence\azure-ai-documentintelligence\README.md
sdk\confidentialledger\azure-security-confidentialledger\README.md
sdk\agrifood\azure-verticals-agrifood-farming\README.md
sdk\anomalydetector\azure-ai-anomalydetector\README.md

[github-actions]

@billwert @g2vinay

[github-actions]

Thank you for your feedback. Tagging and routing to the team member best able to assist.