feat: add headers

[KazuCocoa]

Hm... It seems this does not work in Electron app (I haven't checked via browser type yet tho). in webdriverio. the headers option can customize its HTTP request header. But I guess this electron's one does not...?

Current request headers

POST /wd/hub/session HTTP/1.1
Host: 127.0.0.1:4723
Connection: keep-alive
Content-Length: 216
accept: application/json
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) appium-inspector/2022.1.2 Chrome/91.0.4472.164 Electron/13.6.3 Safari/537.36
content-type: application/json
Sec-Fetch-Site: cross-site
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US

Previously AD override it as https://github.com/appium/appium-desktop/pull/1716