Allow specifying the location of markdownignore file

[Janpot]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything (or linked relevant results below)

Problem

We consolidate our linter ignore rules in a .lintignore file to avoid duplicating them across multiple tools. with remark-cli it's possible to define a --ignore-path but that feature seems to be missing from this extension.

Current solutions

duplicate our rules in .markdownignore

Proposed solutions

Allow setting a ignorePath setting in the vscode extension.

[remcohaszing]

PR welcome.

This needs:

• A change in unified-language-server to support the new configuration opion.
• A change in remark-language-server to document the new configuration option.
• A change in vscode-remark to declare the new configuration option.

[github-actions]

Hi! This was marked as ready to be worked on! Note that while this is ready to be worked on, nothing is said about priority: it may take a while for this to be solved.

Is this something you can and want to work on?

Team: please use the area/* (to describe the scope of the change), platform/* (if this is related to a specific one), and semver/* and type/* labels to annotate this. If this is first-timers friendly, add good first issue and if this could use help, add help wanted.

[astrobrownmusic]

I opened a focused PR for the VS Code extension side of this: declaring the existing language-server ignorePath settings in package.json and documenting them in the README. The unified-language-server and remark-language-server support/docs already appear to be present on current main.

[github-actions]

Hi! This was closed. Team: If this was fixed, please add phase/solved. Otherwise, please add one of the no/* labels.