Add retries to GCS sink healthcheck

[alexander-jiang]

Request to update the data_infra_vector_stable branch, which is used to build the discord_data_vector_base image.

Summary

We've noticed that GCS sink healthcheck in Vector will sometimes fail temporarily (due to timeout) and then will self-recover. The Data Infra team hasn't found a clear reason as to why the healthchecks time-out (e.g. I haven't been able to replicate the healthcheck timeouts in staging), and we want to reduce the impact of ephemeral/noisy healthcheck failures or timeouts on the Vector deployments which are part of our critical event ingestion pipeline. At the same time, we shouldn't completely ignore healthcheck failures.

This PR makes the following changes:

• adds a retry-loop within the GCS sink healthcheck. Instead of only making one attempt, the healthcheck will now make up to 3 attempts to send the HTTP request, with a 5-second delay between each attempt. (Note the overall healthcheck timeout duration is still 10 seconds, so we expect this to make 2-3 attempts per Vector container restart.)
• If any attempt fails, the HTTP response object is printed in logs for debugging purposes. This can help us identify the cause of healthcheck failures (we may be able to identify a root cause and implement a better solution)
• The overall GCS sink healthcheck succeeds as soon as any individual attempt succeeds, avoiding unnecessary retries.

Documentation update:
The PR also updates the patches/README.md file: our Vector build pipeline no longer uses the *.patch files to apply patches onto a commit from the vector repository, but instead builds from a Discord-owned fork of the Vector repository.