Use fs.FS when explicitly given

[doug-threatmate]

Proposed changes

This updates DiskCatalog to use fs.FS when explicitly given by a user via NewFSCatalog.

The existing code half-used fs.FS, but there are a lot of issues with the existing implementation and what needs to be done. After doing a whole lot of testing (and concerns with golang/go#44279), I believe that the best possible implementation is a 2-track one: we support legacy os operations by default, but if someone gives us an fs.FS instance, then we'll use that exactly as they intended it.

Long-term, I hope that the fs.FS semantics are fixed by Go (or at least that a meaningful package gets built that provides full backward compatibility with the os operations).

In my particular case, I have two use cases that both work with these changes:

1. Load files from a directory on disk for local testing. This uses NewCatalog.
2. Load files from a tarball in memory such that the files never touch the disk (Windows Defender and other tools find them and cause all kinds of trouble, and my application really has no business writing to the disk anyway). This uses NewFSCatalog with github.com/quay/claircore/pkg/tarfs to provide the fs.FS interface.

Checklist

• Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[stan-threatmate]

Looks good!

[tarunKoyalwar]

lgtm !

minor update

• removed gologger debug statements ( in cli -debug flag enables debug statements and this flag is usually used to debug template data and not nuclei engine internals )

we are thinking of adding log/slog support soon that will allow selective filtering of different type of logs via enum/custom handler

templateFs was something i was experimenting to primarily load template directory like a virtual file system and abstract various sources via https://github.com/hairyhenderson/go-fsimpl , but it never took off because of glob or some other issue, but anyway thanks for completing the support for fs.Fs

[Mzack9999]

lgtm - nice one!