exclude non required checks from github checks status

[ejoffe]

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Stack:

• fix git spr edit - don't git add -A #508
• new readme #507
• add ability to configure requiredChecks #506
• exclude non required checks from github checks status #505 ⬅
• add --text (-t) to git spr status #504

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⚠️ Part of a stack created by spr. Do not merge manually using the UI - doing so may have unexpected results.