[App Service]: BREAKING CHANGE: Redact connection string values and log warning

[amberwang113]

Related command
az webapp config connection-string set/delete

Description
Necessary to protect potential passwords in webapp connection strings. Redacted outputs of set/delete for the command by setting value for each added connection string to null. Added warning to indicate that behavior has changed and that users should use config connection-string list to view values of the connection strings.

Testing Guide

1. Create webapp (az create webapp)
2. Add a connection string (az webapp config connection-string set)
   azdev test test-webapp-config
   azdev test test-webapp-slot

History Notes

[Component Name 1] BREAKING CHANGE: az command a: Make some customer-facing breaking change
[Component Name 2] az command b: Add some customer-facing feature

---

This checklist is used to make sure that common guidelines for a pull request are followed.

• The PR title and description has followed the guideline in Submitting Pull Requests.

• I adhere to the Command Guidelines.

• I adhere to the Error Handling Guidelines.