🤖 labels: add x:rep labels for awarding reputation

[exercism-bot]

Up until now, we used the x:size label to deviate from the default
reputation that is awarded for a pull request.

This worked well, until we decided to also allow awarding reputation
for opening an issue (but only for large/massive issues), as we already
used the x:size label for an indication of the effort needed to
implement said issue.

To combat this, we decided to switch to using a x:rep label for awarding
reputation, both for pull requests and issues.

This PR adds the x:rep labels.

For backwards compatibility purposes, we still support the x:size
label on pull requests, but recommend using the x:rep label from now
on.

For more information on reputation and how these labels should be used,
check out https://exercism.org/docs/using/product/reputation

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ℹ More info: exercism/org-wide-files@68ae5eb
👁 Tracking issue: exercism/org-wide-files#202

[ee7]

Suggested change

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[ee7]

Maybe we can recreate this PR. Setting as draft so this isn't merged automatically.

See exercism/org-wide-files#204

[ee7]

We'll re-create this.

Context: exercism/org-wide-files#205 (comment)