rgw: refactor D3nDataCache::d3n_io_write to avoid resource leaks

[vedanshbhartia]

1. D3nChunkDataInfo was allocated at the beginning of the function on the heap, and was not freed in case of errors. This memory allocation has been moved to where it is being utilised.
2. cache_file file descriptor was not closed if the write to the file failed. The file close snippet has been moved to the end of the function, and is called if the write fails, or if control flow reaches the end of the function.

Reference: Coverity Defect ID 1510684
https://scan5.scan.coverity.com/reports.htm#v59282/p10114/fileInstanceId=237731707&defectInstanceId=53014748&mergedDefectId=1510684

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[vedanshbhartia]

@yuvalif Is there any issue in closing the file descriptor after adding cache metadata to the cache map?

[yuvalif]

@vedanshbhartia why did you close the PR?

[vedanshbhartia]

@vedanshbhartia why did you close the PR?
We decided on a slightly different solution to this problem (using unique_ptr and a custom destructor), and I was not sure whether we would keep this function. I'll make these changes in a while and update the PR.

[vedanshbhartia]

Github didn't allow me to reopen this PR, so I've opened a new one at #51648