[FEAT] - add "--update" option

[ximenesyuri]

Description

The suggestion is to incorporate an option --update or just update to self-update the mgc to its latest version.

The option could:

1. collect the underlying architecture in which mgc is installed (say from lscpu or from uname -m);
2. collect its current installation dir (with ${BASH_SOURCE[@]%/*}, or some analogue for other shells)
3. do a bootstrap to get the latest version of mgc from its official source: the latest release of this repo.

Motivation

Since the project is constantly improving, updates may be needed frequently. This option would make users' lives easier.

Workaround

A naive attempt to provide a user-side extension for the mgc in order to include this feature can be observed here:

• https://github.com/ximenesyuri/mgc/tree/main/utils/mgc-update

There are already two open pull requests proposing solutions:

1. feat: script to help update mgc #19
2. feat: easy install/upgrade cli #18