feat: gsutil file format mutator for same bucket

[RahulDubey391]

Hi Folks,

looking for the feature for allowing changing file formats in the same bucket through command line interface.

The bucket can have 1000's of files having same format for example:

• "application/octet-stream" which can be morphed to another format like "application/x-log".
• Command should also allow changing the file formats based on stored format field and not only the extension of the file.
• Command should work on the same bucket. There can be a temp bucket just for moving from one format and getting in another format.
• Lastly, the command line should also provide a list of the files that got changed.

Thanks!