Global const for KeyFileOption (CLI)

[louib]

Motivation and context

Same option is defined in most of the CLI commands. Also, more global options might appear in the future (--no--password, --silent, --yubikey, for example).

How has this been tested?

unit tests.

Types of changes

• ✅ Refactoring

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]

[louib]

@droidmonkey rebased this one after merging #2507

[droidmonkey]

After rebasing this, I realized there should really be a common method to opening the database within the CLI. We are repeating the call to

auto db = Database::unlockFromStdin(databasePath,
                                        parser.value(Command::KeyFileOption),
                                        parser.isSet(Command::QuietOption) ? Utils::DEVNULL : Utils::STDOUT,
                                        Utils::STDERR);

Many many times with the same inputs.

[phoerious]

That method needs to be refactored out of the Database class anyway.