Support --config (custom config filepath)

[chrisgrieser]

The typos cli supports --config to use a specific config file. Having such an option also for the LSP could be quite useful as well?

[tekumara]

Great idea!

[dsully]

+1 - would love to be able to set this globally for projects that don't have a config.

[tekumara]

@dsully I can make this work the same as typos --config ie:

• when a project doesn't have a config, use the custom config file
• when a project has a config, merge the custom config file with the project's config. The custom config takes precedence when a setting is declared in both (ie: as per reference.md)