0.7.0 beta testing fixes

[brettimus]

This PR includes the following fixes:

Conditionally access the window object for push gateway exporter

The push gateway exporter has a reference to window, which won't be defined for serverless functions. I added a check to make sure window was defined before adding/removing event listeners to it.

Do not pass MAX_SAFE_INTEGER as an interval value

The push gateway and otlp-http exporters both used Number.MAX_SAFE_INTEGER for the PeriodicExportingMetricReader export interval. Because this value is ultimately passed to setInterval, we need to use a smaller value instead.

This is because setInterval and setTimeout represent the timeout value as a 32bit unsigned integer. So, MAX_SAFE_INTEGER will cause wrapping, leading to some funkiness. (See: MDN docs)

Wrap Deno.cwd() in a try/catch

It's possible for Deno.cwd to be defined (and even return "function" when passed to typeof), but if the Deno script was not given permissions to access the filesystem, then calling Deno.cwd() will throw an error. I uncovered this is in Supabase/Deno Deploy.

So, I added a try-catch there... as well as for process.cwd, just to be defensive (could remove that upon request)