Enhance COS event Subscription doc for Cos object prefix and suffix

[karanibm6]

Backgroud :

Existing doc : https://cloud.ibm.com/docs/codeengine?topic=codeengine-eventing-cosevent-producer

While creating the cos event subscription in codeengine, one can specify a prefix and a suffix for the objects in the COS buckets. It just mentions the term prefix and suffix, but doesn't tells you what it supports and what it doesn't support.

While testing out the various possibilities with prefix and suffix, we observed :

• One cannot use the wildcards while specifying the prefix/suffix. (For e.g if you put *.json as suffix, it won't work for all json files. it would only work if you just put json as suffix). Also regular expressions are also not supported.

• One more point is that the file name includes its extension. For e.g if someone specifies json as suffix, then the event will be handled for files like abc.json, not for abcjson.txt.