[BUG][typescript-fetch] Base Path can't be set to relative path

[mosino]

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When the server url is set to a relative path, in the generated source files it will be prefixed with "https://localhost"

openapi-generator version

latest

OpenAPI declaration file content or url

"servers": [
    {
      "url": "/my-api"
    }
  ]

Generation Details

openapi-generator-cli generate --skip-validate-spec --input-spec ./my-api.json --generator-name typescript-fetch --output gen/my-api --config my-api-config.json

my-api-config.json

{
  "npmName": "my-api",
  "npmVersion": "1.0.0",
  "snapshot": false,
  "supportsES6": false,
  "modelPropertyNaming": "original"
}

Steps to reproduce

Run the above command on a yaml file with server url set to a relative path

Related issues/PRs

#2731
#2731

[macjohnny]

@mosino would you like to fix this?