Allow exceptions to be configured

[khiga8]

In some projects, the defaults we have configured for the no-generic-link-text rule do not make sense. We should allow exceptions to be configured.

With this update, exceptions can be configured for the no-generic-link-text rule like so:

"no-generic-link-text": { "exceptions": ["link"] } 

In particular, this need surfaced in the Primer ViewComponents repo, where we don't want to flag [Link](primer.style/view_components/components/link) where Link refers to a component, rather than a generic text. We determined that allowing exceptions is the better route to go for now.

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[khiga8]

Since nearly everyone in my team is OOO and this was reviewed by Jon, I merged this PR!