[SE-50] Deprecate external directory config option

[dremin]

Summary

Given that the contacts feature is the scalable way to save contacts, and that the custom-transfer-directory integrates with the contacts feature, this deprecates the flex-config-based external directory entry support in custom-transfer-directory.

The functionality is still there in case a customer using it updates their copy of the template. A warning log has been added in that case.

Checklist

• [x] Tested changes end to end
• [x] Updated documentation
• [x] Requested one or more reviewers

[github-actions[bot]]

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[trogers-twilio]

@dremin Does the "contacts" feature support toggling cold or warm transfer per record like the Flex config external directory does? I didn't see that option in the "contacts" feature docs, but I may be missing it.

[dremin]

@dremin Does the "contacts" feature support toggling cold or warm transfer per record like the Flex config external directory does? I didn't see that option in the "contacts" feature docs, but I may be missing it.

You are correct, it does not.