Added action configuration values

[benoitgoyette]

Fixes and adds arguments that are passed to gitleaks application.

Fixed GITLEAKS_CONFIG that didn't seem to be used.

While testing, I discovered that passing multiple arguments in the same string does not yield the same result and appending multiple arguments

args.push(`-c ${process.env.GITLEAKS_CONFIG}`);  // raises an error

args.push("-c", process.env.GITLEAKS_CONFIG);      // works

Added these options

• GITLEAKS_SILENT, if true removes the -v --redact arguments
• GITLEAKS_NO_GIT, if true sets the --no-git argument, discards the other versions and baseline options.
• GITLEAKS_BASELINE_FILE, if set, added the -b path/file argument.
• GITLEAKS_LOG_LEVEL, if set, changes the log level

[kawaxi]

@benoitgoyette