nuclei: `nuclei` fails to start when `~/.config` is not writable

Nuclei version:

nuclei 2.9.2 (built from https://github.com/projectdiscovery/nuclei/archive/v2.9.2.tar.gz)

Current Behavior:

nuclei fails to start when the .config directory under home directory is not writable:

$ nuclei -target google.com -t test.yaml
[ERR] failed to create config directory at /Users/brew/.config/nuclei got: mkdir /Users/brew/.config/nuclei: operation not permitted
[ERR] failed to write config file at /Users/brew/.config/nuclei/.templates-config.json got: [:RUNTIME] could not create nuclei config directory at /Users/brew/.config/nuclei <- mkdir /Users/brew/.config/nuclei: operation not permitted

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/_/ /_/\__,_/\___/_/\___/_/   v2.9.2

		projectdiscovery.io

[INF] nuclei-templates are not installed, installing...
[INF] nuclei-templates are not installed, installing...
[FTL] Could not create runner: [:RUNTIME] could not create config file <- open /Users/brew/.config/nuclei/reporting-config.yaml: no such file or directory

Expected Behavior:

The .config directory under home directory can be unwritable for some reason. For instance, when nuclei is being run in a sandboxed environment, or when the .config is deliberately made read-only.

nuclei should be able to accept a config directory other than the default one; or alternatively, it should not always attempt at creating the directory at startup.

It would probably help to have a flag -config-dir or an environment variable NUCLEI_CONFIG_DIR that allows overriding the default config directory.

Steps To Reproduce:

1. chmod -rx ~/.config
2. nuclei -target google.com -t test.yaml
3. See error.

Anything else:

This error was observed while packaging nuclei for Homebrew in https://github.com/Homebrew/homebrew-core/pull/128819. Homebrew’s tests are executed in a temporary sandboxed environment, where the HOME environment variable is changed to a temporary directory and everything outside is not writable. However, getDefaultConfigDir’s implementation uses Go’s os/user package to determine the home directory; os/user retrieves the home directory information from the system interface (pwd.h), which does not seem to respect the sandbox settings.