feat: auto browser download

[KuznetsovRoman]

What is done

Added ability to automatically download browsers and/or webdrivers for these browsers.

Supported browsers to download:

• chrome > 73
• firefox

Supported drivers to download:

• chromedriver (for chrome)
• geckodriver (for firefox)
• edgedriver (for edge)

With "--local" (or gridUrl: "local") and webdriver protocol, webdiver instances are automatically run for these browsers:

• chrome (>73)
• firefox
• edge (if the browser itself is installed. Driver will be installed automatically)
• safari (mac only)

When launching tests with "--local" (and optionally webdriver protocol) all supported browsers/drivers will be installed automatically, if necessary. With "--local" we at all cost are trying to avoid network requests to google/mozilla/... servers.

Example

• Set up a testplane config, using webdriver protocol and describe some chrome/firefox browsers with defined versions
• Launch eigher using npx testplane --local, either by setting "gridUrl": "local"

In order to just download browser, npx testplane install-browsers could be used. This way we also check if our browsers are up-to-date, so if we have 114.0.5696.0 downloaded and user wants chrome@114.0, we check for newest chrome@114.0 version and see it is "114.0.5735.133". Then this new version is downloaded

• If used without arguments, all of the config browsers will be installed
• If argument is browserId from config, the corresponding browser will be installed
• If argument is browserName>@<browserVersion, it will be installed. These can be combined: npx testplane install-browsers my-chrome chrome@115

Directory to save testplane browsers and drivers can be set with TESTPLANE_BROWSERS_PATH env variable. By default, ~/.testplane is used.