Add tombi linter

[jnk22]

I added a config for Tombi.

Notes

• There is an offline mode available with the --offline option. I have not seen this being used by any other formatter, therefore I did not use this for Tombi.
• Tombi uses the filename for extra diagnostics. Is getting the input via stdin generally preferable? If so, this could be done similar to what perlimports.lua does, but using it without seems more straightforward.

Resolves #836

[mfussenegger]

Tombi uses the filename for extra diagnostics. Is getting the input via stdin generally preferable?

Generally yes, because it gives users more flexibility in how to use the linter - not just on save, but on unsaved content too.

But starting without stdin is also fine. If people want to have stdin support the linter can always be extended.