Code insights backend: default to `archived:no` and `fork:no` filters on backend searches – help text

Created by: Joelkw

We have a strong POV (based on customer feedback + behavior so far) that customers expect insights to essentially match Sourcegraph search GUI.

The Sourcegraph search GUI currently defaults to searching forks and archived repositories, however, because when you search explicitly using a repo: tag that's how it works (see more context from @slimsag there).

Based on @slimsag 's knowledge of why we default to excluding forks and archives from sourcegraph GUI searches now, it makes sense to maintain this default in code insights – no reason to give you needless duplicates.

One positive note/one note to maintain: explicitly passing fork: or archived: filters in the data series should always be honored (so when we change the default to these both being off, it should still be possible to manually set them on). This is how it works now, which is "positive" because it means even if customers don't want forks in their results, before we change the defaults we just have to advise them to include a fork:no and archived:no in their data series query.

Example: without archived+forks 32 results and with archived+forks 33 results

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Edited by @unclejustin

Action Items

As per @felixfbecker's comment here https://github.com/sourcegraph/sourcegraph/issues/24023#issuecomment-900152127

1. Update help text with "This includes archived and forked repositories, add archived:no and forked:no to exclude them."