feat: Add BOM indicator to encoding component

[sergiuser1]

Inspired by vim-airline, it adds [BOM] to the encoding if the file uses byte-order mark

[shadmansaleh]

Does vim/neovim's builtin statusline show this by default? if not can you put it behind an option, set default to false?

[sergiuser1]

By default it doesn't have anything about file encoding, I found this about making a custom component: https://stackoverflow.com/a/10416234/11710862

I'll add the option and some tests and will update the PR.

[generated-files-bot[bot]]

Warning: This pull request is touching the following templated files:

• doc/lualine.txt - lualine.txt is generated from README.md. Make changes there instead.

[sergiuser1]

@shadmansaleh I've made it optional with the default being false, and I've added tests.

[sergiuser1]

@shadmansaleh ping

[shadmansaleh]

Thanks. Sorry for the late reply.

[sergiuser1]

Thanks!