test(e2e): prove bucket config survives rc.5 upgrade and rollback
Add two upgrade-compatibility scenarios pinned to the on-demand-migration
series' on-disk surfaces: BucketMetadata's 44 -> 46 msgpack keys, the
fail-closed bucket-config reads of rustfs#7172, the encryption-gated PUT
path of rustfs#7183, and the default-on migration module of rustfs#7089.
The upgrade case writes versioning, SSE-S3 default encryption, a validated
replication target plus rule, lifecycle, tags, quota, a public access block,
a bucket policy and an object lock configuration with the pinned previous
release, then asserts each one reads back unchanged on the current build,
that list-remote-targets still reports the target, that writes to the
encrypted and plain buckets keep their encryption posture, that every
pre-upgrade object including a multipart one is byte-identical, and that an
unconfigured bucket reports no migration and still answers NoSuchKey.
The rollback case is the reverse: the current build writes the 46-key blob
and the previous release must decode it by skipping the two unknown keys.
Zhengchao An