Feat: add i18n support and chinese translations

[kap1bala]

Summary

This pull request integrates internationalization capabilities into the WLED web installer, making it accessible to a wider audience. It introduces a new JavaScript file to manage translations and updates the main HTML page to dynamically display content in different languages, starting with English and Simplified Chinese. The changes allow users to select their preferred language, which is then saved for future visits.

Related Issue

close #66

Review bot

kapibala/WLED-WebInstaller#3

[lost-hope]

I see two differences in the powered and Cors lines between the english and chinese variant. is that there to have a better translation?

[kap1bala]

I see two differences in the powered and Cors lines between the english and chinese variant. is that there to have a better translation?

Yes, some sentences have different word orders in Chinese and English. To preserve the <a> tags, I have splitted some sentences into multiple segments for translation:

https://github.com/kap1bala/WLED-WebInstaller/blob/cef9e4503d4b7251c36e3ab5dc2f2c1d00c8cd8e/index.htm#L145-L151

the translations looks like:

English	Chinese
Powered by ESP Web Tools	ESP Web Tools 强力驱动

Using innerHTML would avoid splitting, but it carries potential XSS risks, maybe there would be a better solution, I'd love to consider any suggestions :)