fix(gatsby-cli): lower required react version

[pieh]

Requiring latest react version in gatsby-cli (for ink) causes trouble with npm installs - if user specified react version doesn't satisfy >= 16.8 constraint then it seems like npm can't properly resolve node_modules hierarchy

This does not take care of #19827 completely, but it limits scenario when this error will happen (with this change it should only happen when user specified version of react is in range >= 16.3 && < 16.8 (instead of >= 16.3 && 16.12):

npm WARN ink@2.7.1 requires a peer of react@>=16.8.0 but none is installed. You must install peer dependencies yourself.

gatsby-shopify-starter@0.1.0 /Users/misiek/test/marcuswelds-gatsby-test
├─┬ UNMET PEER DEPENDENCY gatsby@2.19.18-cli-react-from-ink.35
│ └─┬ gatsby-cli@2.8.30-cli-react-from-ink.162
│   └── UNMET PEER DEPENDENCY react@16.12.0 
└── react@16.7.0 

16.8.0 version is needed by ink and our ink logger (we use hooks), so can't go lower in this PR

Commits where cherry-picked from scratched attempt at fixing it completely ( #21508 )

[pvdz]

Trusting your judgement

[pieh]

I published canary and running some manual tests to make sure react@16.8.0 is enough for CLI

[pieh]

Ok, manual testing with react@16.8.0 went well, so I'll go ahead and merge it

[pieh]

Published gatsby-cli@2.8.30 and gatsby@2.19.18