Reduce memory usage of SecretScanner

[Ramanan Ravikumar]

SecretScanner takes >250 mb of memory when scanning hosts with huge number of files

[Ramanan Ravikumar]

#28
It was saving list of all files to process in a slice which was taking lot of memory beyond 300k entries.
Now optimized that part to process the files inside filepath.Walk as and when we get a file.

[sandman137]

What is the current memory usage for scanning a large container image (say 1g+)?

[Ramanan Ravikumar]

Now it takes ~60 mb for all scans