telemetry: add "initialized" lsp stage aws#1001

## Problem
LanguageServerSetupStage does not include initialized stage which is
needed in VS and LSP protocol.
VS had an issue where needed to diagnose and measure customer failures
that occur after the lsp was successfully started but the IDE failed to
make a successful "initialized" communication.
For reference, LSP clients send an
"[initialize](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialize)"
message back and forth, and then they send an
"[initialized](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#initialized)"
message back and forth. The related pr is
[here](aws/aws-toolkit-visual-studio-staging#2339).

## Solution
I add the initialized stage in common's definition. The initialize stage
is defined as handshake in common's definition so we do not need to make
any modification for initialize.

Author: XiaoxuanLu

telemetry/definitions/commonDefinitions.json

@@ -1708,6 +1708,7 @@
                 "validate",
                 "launch",
                 "handshake",
+                "initialized",
                 "all"
             ],
             "description": "The stage of the LSP setup process"