Create or update comments for benchmark results

[antiagainst]

This is a follow up to #6124,
where we categorized and sorted benchmark result tables.
But it's still noisy given we are posting many abbreviated
summary tables. This tries to reduce that by trying to find
the last previous comment from the bot's account and
update that.

Also, using issue API endpoints instead of pull request ones,
in the hope to avoid putting the bot as a "reviewer".

Only the last commit matters.

[iree-github-actions-bot]

Abbreviated Benchmark Summary

@ commit d66e7e070b3da7bf2ee3ada4cd12161ef53e9622 (vs. base af7dfeb5394d92b2df1d5e6014d52fed9d5a07ff)

Similar Benchmarks

Benchmark Name	Average Latency (ms)	Median Latency (ms)	Latency Standard Deviation (ms)
MobileNetV2 [fp32,imagenet] (TensorFlow) kernel-execution with IREE-Vulkan @ SM-G980F (GPU-Mali-G77)	22	22	1
MobileNetV2 [fp32,imagenet] (TensorFlow) 3-thread,little-core,full-inference with IREE-Dylib @ SM-G980F (CPU-ARMv8.2-A)	872	872	6
MobileNetV2 [fp32,imagenet] (TensorFlow) 1-thread,little-core,full-inference with IREE-Dylib @ SM-G980F (CPU-ARMv8.2-A)	1255	1256	6

[Top 3 out of 36 benchmark results showed]

For more information:

• Full benchmark result tables
• Buildkite build

[antiagainst]

Thanks Scott for the suggestion. Looks using API endpoints for issues does work here. There is only one comment now and it was edited for the second build. :)

[ScottTodd]

nice, and thanks for pointing out the edit history @benvanik !