feat(service): Add metrics for multipart upload operations

[lcian]

This adds latency metrics for all multipart operations, all tagged with usecase: multipart.initiate.latency, multipart.upload_part.latency, multipart.list_parts.latency, multipart.abort.latency, and multipart.complete.latency.
Note that these are distributions but we can also chart them as counts/rates to count such requests.
We also track two specific sizes: multipart.upload_part.size and multipart.complete.part_count.

Additionally, we reuse the put.size which we use for normal PUTs to record the size of the assembled object upon multipart_complete.
The reason we reuse that metric is that right now we only use it to create histograms for the size we're storing, so I think it's actually good to have them together.
A new tag upload_type lets us distinguish between the kind of upload that recorded a put.size (direct or multipart).

Close FS-360

[linear-code]

FS-360

[cursor]

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[matt-codecov]

address robot comments