[typescript] fix: allow 'additionalProperties: true' at top level

[tcrasset]

I was getting the following error

Exception in thread "main" java.lang.RuntimeException: Could not process model 'AvatarizationBatchParameters'.Please make sure that your schema is correct!
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:529)
	at org.openapitools.codegen.DefaultGenerator.generate(DefaultGenerator.java:950)
	at org.openapitools.codegen.cmd.Generate.execute(Generate.java:511)
	at org.openapitools.codegen.cmd.OpenApiGeneratorCommand.run(OpenApiGeneratorCommand.java:32)
	at org.openapitools.codegen.OpenAPIGenerator.main(OpenAPIGenerator.java:66)
Caused by: java.lang.ClassCastException: class java.lang.Boolean cannot be cast to class io.swagger.v3.oas.models.media.Schema (java.lang.Boolean is in module java.base of loader 'bootstrap'; io.swagger.v3.oas.models.media.Schema is in unnamed module of loader 'app')
	at org.openapitools.codegen.languages.TypeScriptClientCodegen.addAdditionPropertiesToCodeGenModel(TypeScriptClientCodegen.java:505)
	at org.openapitools.codegen.DefaultCodegen.updateModelForObject(DefaultCodegen.java:2893)
	at org.openapitools.codegen.DefaultCodegen.fromModel(DefaultCodegen.java:3111)
	at org.openapitools.codegen.DefaultGenerator.processModels(DefaultGenerator.java:1329)
	at org.openapitools.codegen.DefaultGenerator.generateModels(DefaultGenerator.java:524)
	... 4 more

when having the following OpenAPI schema

"AvatarizationBatchParameters": {
        "title": "AvatarizationBatchParameters",
        "required": ["training_dataset_id"],
        "type": "object",
        "properties": {
          "training_dataset_id": {
            "title": "Training Dataset Id",
            "type": "string",
            "format": "uuid"
          },
        },
        "additionalProperties": true
      },

where we have additionalProperties: true at the top level which is a valid spec it seems.

This is related to #13003, but it had additionalProperties that was nested.

Also related is the following issue, but is not specific to typescript:
#9282

The fix was simply to conform to how all the other typescript generators do it, e.g. TypeScriptAxiosClientCodegen.java

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[tcrasset]

@TiFu (2017/07) @taxpon (2017/07) @sebastianhaas (2017/07) @kenisteward (2017/07) @Vrolijkx (2017/09) @macjohnny (2018/01) @topce (2018/10) @akehir (2019/07) @petejohansonxo (2019/11) @amakhrov (2020/02) @davidgamero (2022/03) @mkusaka (2022/04)

Please review :)

[macjohnny]

LGTM
Thanks for your contribution