reduce dependabot frequency from weekly to monthly, get rid of email spam

Summary

Also ignore patch and minor bumps for dependencies, and ignore patch bumps for github actions. This will let us focus on major updates.

Docsify is a static website, there's isn't much of a security concern with checking every patch bump. We aren't making a server application for people to put across their servers, we're simply reading markdown and outputting HTML on the client, nothing very critical at all, so we don't need to spend so much time with noisy updates.

Related issue, if any:

What kind of change does this PR introduce?

Build-related changes Repo settings

For any code change,

[x] Related documentation has been updated, if needed
[x] Related tests have been added or updated, if needed

Does this PR introduce a breaking change?

Tested in the following browsers:

N/A

docsifyjs / docsify