Allow configuration of ad load timeout for Google IMA plugin

[tch-vidangel]

Enable setting a custom ad load timeout for the Google IMA plugin via the ad configuration. By default, IMA uses an 8-second timeout if no option is provided, but this can now be adjusted as needed.

[tvanlaerhoven]

@tch-vidangel Thank you for your contribution!

[tvanlaerhoven]

@tch-vidangel I didn't check in detail yet, but there is a build issue on iOS picked-up by our e2e testing:

[react-native-theoplayer-tvOS] Compiling THEOplayerRCTView+Ads.swift
Error: cannot assign value of type 'Int' to type 'TimeInterval' (aka 'Double')
            imaRenderSettings.loadVideoTimeout = adLoadTimeout
                                                 ^~~~~~~~~~~~~

Please take a look; or otherwise we can check as well.

[wvanhaevre]

Perhaps also add a changelog entry to the CHANGELOG.md