Add web support

[doppio]

It would be nice if this plugin supported the Freshdesk web SDK through the same API as it uses for iOS/Android. With Flutter web support in beta, it would be useful to make this plugin more cross-platform.

I may eventually implement this myself when I need it for my project, but that won't be for 6-12 months.

[doppio]

@chaitanya-y You should file a new issue for that or ask on Stack overflow, this issue is about adding web support to the package.

[fayeed]

@doppio I haven't looked at the Freshchat web SDK or don't know much about it but I might integrate if enough people request it.

[kaumudpa]

It looks like WEB integration is needed.