fix: add overwrite: true to overwrite on existing file

[hiddewie]

This is a followup PR of #295. Concurrent downloads work well, but the filesystem move call throws an error in fs-extra when the file already exists... It should replace it of course.

Reference documentation: https://github.com/jprichardson/node-fs-extra/blob/master/docs/move-sync.md

Sorry I did not notice it in previous testing. All the tests currently mock the filesystem library, so I cannot simulate an existing file.

Example (anonymized) output of current 2.2.0 version:

...
Compile the schemas /XXXXXX/har.schema.yaml to /XXXXXX
Compiling /XXXXXX/har.schema.yaml with name har.
Compile the schemas /XXXXXX/index.schema.yaml to /XXXXXX/generated
Compiling /XXXXXX/index.schema.yaml with name Index.
Compile the schemas /XXXXXX/configuration.schema.yaml to /XXXXXX/generated
Compiling /XXXXXX/configuration.schema.yaml with name BotConfiguration.
Download 5.0.1 ...
Download 5.0.1 ...
Downloaded 5.0.1
/XXXXXX/node_modules/fs-extra/lib/move-sync/move-sync.js:25
  if (fs.existsSync(dest)) throw new Error('dest already exists.')
                           ^
Error: dest already exists.
    at doRename (/XXXXXX/node_modules/fs-extra/lib/move-sync/move-sync.js:25:34)
    at Object.moveSync (/XXXXXX/node_modules/fs-extra/lib/move-sync/move-sync.js:17:10)
    at WriteStream.<anonymous> (/XXXXXX/node_modules/@openapitools/openapi-generator-cli/main.js:863:74)
    at WriteStream.emit (node:events:390:22)
    at finish (node:internal/streams/writable:741:10)
    at finishMaybe (node:internal/streams/writable:723:9)
    at afterWrite (node:internal/streams/writable:510:3)
    at onwrite (node:internal/streams/writable:483:7)
    at node:internal/fs/streams:392:5
    at FSReqCallback.wrapper [as oncomplete] (node:fs:663:5)
[main] INFO  o.o.codegen.DefaultGenerator - Generating with dryRun=false
[main] WARN  o.o.c.ignore.CodegenIgnoreProcessor - Output directory does not exist, or is inaccessible. No file (.openapi-generator-ignore) will be evaluated.
[main] INFO  o.o.codegen.DefaultGenerator - OpenAPI Generator: typescript-axios (client)
[main] INFO  o.o.codegen.DefaultGenerator - Generator 'typescript-axios' is considered stable.
[main] INFO  o.o.c.l.AbstractTypeScriptClientCodegen - Hint: Environment variable 'TS_POST_PROCESS_FILE' (optional) not defined. E.g. to format the source code, please try 'export TS_POST_PROCESS_FILE="/usr/local/bin/prettier --write"' (Linux/Mac)
...

[github-actions]

🎉 This PR is included in version 2.2.1 🎉

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