This commit moves the repository-s3 fixture test added in #29296 in a
new `repository-s3/qa/amazon-s3` project. This new project allows the
REST integration tests to be executed using the real S3 service when
all the required environment variables are provided. When no env var
is provided, then the tests are executed using the fixture added
in #29296.
The REST tests located at the `repository-s3`plugin project now only
verify that the plugin is correctly loaded.
The REST tests have been adapted to allow a bucket name and a base
path to be specified as env vars. This way it is possible to run the tests
with different base paths (could be anything, like a CI job name or a
branch name) without multiplicating buckets.
Related to #29349
7ae3b3b155