copyblocks: add support for S3-compatible buckets and object storage migration

[andyasp]

What this PR does

copyblocks currently supports GCS->GCS and ABS->ABS server-side copies. This change adds:

• S3->S3 server-side copy support
• client-side copy support for copies to be performed across services (source GET chained to destination PUT)
• the ability to toggle between server-side copies and client-side copies if both buckets are on the same service

so the new support looks like {ABS, GCS, S3} -> {ABS, GCS, S3}.

Notably --service was replaced with --source-service and --destination-service, since the services may not be the same.

I have not finished testing these changes against real buckets yet, so I'm opening this as a draft.

Tests Performed:

• S3->GCS
• GCS->S3
• S3->ABS
• ABS->S3
• S3->S3 (client-side)
• S3->S3 (server-side, tested locally with minio due to permissions)

The goal of this testing was line coverage by having each service be both a source and a destination in client-side copies and to exercise that the S3 client expects to be passed a correct content length during Upload.

Which issue(s) this PR fixes or relates to

Fixes: N/A

Checklist

• Tests updated
• Documentation added
• CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[charleskorn]

Overall LGTM, thanks @andyasp!

[andyasp]

Thanks for keeping me honest with message consistency @charleskorn, those nits were helpful.

[charleskorn]

Thanks for addressing my feedback @andyasp!