Exact match when deleting stream

[trueleo]

Description

When deleting a logstream from s3 avoid deleting other prefixes which starts with same stream_name for which delete request was made.

For example, when deleting stream named test, such streams are also deleted because they share same prefix test
teststream
testlongrun
testapplication

Fix:
Use delimiter at the end of stream name so that only those prefix are matched where stream name is exactly first component of path on s3. i.e test/ instead of test. This will match only logstreams named test.

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.