feat: i18n support for mdbook

[dpinones]

This PR adds support for the i18n mdbook extension.

• Added a script translation.sh to facilitate the work.
• The CI has also been modified to use Rust's cache. The CI always builds the English version first and then the translations.
• When modifying a translation, only the po files will be changed. The book's structure remains completely intact.

To create this PR, I based it on the Beerus Book and Cairo Book.

It's already functional in a test repository:
Repository: https://github.com/dpinones/starknetbook-test
Actions: https://github.com/dpinones/starknetbook-test/actions
Book: http://dpinones.com/starknetbook-test/

[dpinones]

cc: @omarespejel @Nadai2010 @cryptonerdcn

[cryptonerdcn]

Good job!
I'd like to share some exps about the mdbook.

1. Seems like if generates the message.pot from different environments, the .po file also changes. It also happened in Dojo-book [i18n] Add Japanese translation for Dojo book. dojoengine/book#53 (comment) but we don't know why. This can cause some texts to not be included in the .po file.
2. In my Mac, try to run generate language .po file command will cause an error like this:

po/messages.pot:964: duplicate message definition...
po/messages.pot:3: ...this is the location of the first definition

google/mdbook-i18n-helpers#64. It is still not been fixed so if you got the same error, you need to delete 954 to 965 manually. It looks like:

#: src/ch01-00-getting-started.md:13
#: src/ch01-00-getting-started.md:127
#: src/ch02-07-starknet-js.md:11
#: src/ch03-00-architecture.md:26
#: src/ch03-02-sequencers.md:52
#: src/ch03-02-sequencers.md:211
#: src/ch03-04-nodes.md:66
#: src/ch03-04-nodes.md:350
#: src/ch03-04-nodes.md:420
#: src/ch03-05-layer-3.md:18
msgid ""
msgstr ""

[cryptonerdcn]

BTW: I also add Chinese `.po` file to this. Waiting for the merge.

[Nadai2010]

@dpinones @cryptonerdcn This is great, what a great community... Since the merge has been in place we have organized ourselves by language and we will do it with our best effort.

[omarespejel]

Thank you so much, @dpinones! Your contribution is outstanding and paves the way for greater collaboration with communities where @Nadai2010 and @cryptonerdcn play pivotal roles 🙏

I've merged it. A huge thanks once again for your invaluable input! I'll be highlighting this along with recent contributions from @dbejarano820 and @devnet0x in an upcoming tweet. Truly, we have an incredible community!

[Nadai2010]

Thank you @omarespejel for the words, here I leave a small update on the tabs

Tabs book.toml: #208

I'm going to start the translation

[omarespejel]

Amazing @Nadai2010!! Thank you! i just merged your PR 🙏