fix typescript node default enum

[GuyGitzMagen]

• Default enum value and type are seperated by .
• classname is added to enum default property

This is a fix for the bug mentioned here #12634.
I changed the default enum value to be ., and edited model.mustache template accordingly.
For testing I used the following yaml schema and generation command. I made sure that before the fix the client wasn't generated correctly and that the problem was solved after the fix.

Fixes #12634

Opeanapi schema:

openapi: "3.0.0"
info:
  version: "1.0.0"
  title: "Test default enum value"
paths:
  /eat:
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/Fruit"
      responses:
        200:
          description: "Yummy"

components:
  schemas:
    Fruit:
      type: "object"
      properties:
        fruit:
          type: "string"
          enum: [
              "melon",
              "apple"
            ]
          default: "apple"

Generation command:

openapi-generator-cli generate -g typescript-node -i openapi.yml --additional-properties=npmName=example

Committee mentions: @TiFu @taxpon @sebastianhaas @kenisteward @Vrolijkx @macjohnny @topce @akehir @petejohansonxo @amakhrov @davidgamero @mkusaka

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[macjohnny]

LGTM