Build pipeline and e2e test scenario improvements

[twometresteve]

Goal

Makes the formatting of the Buildkite pipeline more consistent and improves some of the Cucumber step uses.

Design

These steps are no longer needed as Maze Runner checks them all:

the trace "Bugsnag-Sent-At" header matches the regex "^\d\d\d\d-\d\d-\d\dT\d\d:\d\d:\d\d\.\d\d\dZ$"
a span field "startTimeUnixNano" matches the regex "^[0-9]+$"
a span field "endTimeUnixNano" matches the regex "^[0-9]+$"

I've used the I wait to receive a span named {string} step in various locations as it provides better diagnostics if it fails than a simple wait for a number of spans.

Testing

Covered by CI.

[bugsnagbot]

Android notifier sizes

Format	Size of apk (kB)
APK	614.94
APK with Bugsnag	745.86

Android notifier size impact

Format	Size impact of Bugsnag (kB)
APK	130.92
Minified APK	55.88

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