Bump Cloud Trace library to v1.8.0

[damemi]

Fixes #208

This bumps the cloud trace client to v1.8.0, which offers default batch retry on failed writes.

Currently the trace client retries failed calls for CreateSpans but not BatchWriteSpans.

[dashpole]

Should we open an upstream issue asking for the default to be changed? Or ask why the default is set the way it is?

If we can avoid adding a new config surface, that seems best. It also would seem odd for us to have a different default from the upstream library.

[damemi]

Upstream issue raised at googleapis/google-cloud-go#7184

[damemi]

update: we implemented this as a default setting in the upstream trace client instead. but, I think we can still use the unit tests I added here to make sure attempts are retried. once the upstream generated clients land, I'll use this PR to bump the dependency and add these tests. Holding until then

[codecov]

Codecov Report

Merging #550 (8f4a511) into main (9c0f81b) will increase coverage by 0.00%.
The diff coverage is 37.50%.

@@           Coverage Diff           @@
##             main     #550   +/-   ##
=======================================
  Coverage   64.68%   64.68%           
=======================================
  Files          38       38           
  Lines        4281     4282    +1     
=======================================
+ Hits         2769     2770    +1     
  Misses       1399     1399           
  Partials      113      113           

Impacted Files	Coverage Δ
...er/collector/integrationtest/testcases/testcase.go	82.87% <ø> (ø)
exporter/collector/logs.go	41.23% <ø> (ø)
exporter/collector/metrics.go	67.68% <ø> (ø)
exporter/metric/metric.go	72.38% <ø> (ø)
exporter/trace/trace.go	90.90% <ø> (ø)
exporter/trace/trace_proto.go	64.73% <ø> (ø)
...er/collector/integrationtest/protos/fixtures.pb.go	42.48% <28.57%> (ø)
exporter/collector/traces.go	70.00% <100.00%> (+0.61%)	⬆️
...lector/internal/datapointstorage/datapointcache.go	83.33% <0.00%> (ø)

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[damemi]

Working on deprecated import path migration (https://github.com/googleapis/google-cloud-go/blob/main/migration.md)...