Shared configuration to extend from

We're currently copy-pasting a lot of config across our monorepo packages (and indeed wider in devops). Some consistent core basis would be useful to extend off of here. Unlikely to make a one-size-fits-all, as e.g. react vs non-react things need different plugins etc.

• eslint config
• prettier config
• tsconfig

Also review if the ignores can be handled in any easier way as a part of this

• eslintignore, prettierignore
• gitignore?
• npmignore?