un-scoped env conflits

[JoueBien]

process.env.LOG_LEVEL is conflicting with our existing environment config.

initialising the SDK fails with:

 ⨯ [Error: default level:verbose must be included in custom levels] {
  page: '/'
}

Can the packages environment variables be scoped so that they won't conflict with anyones existing environment naming?
for example EPPO_LOG_LEVEL.

Please also note for Next.js (running client side only) LOG_LEVEL or EPPO_LOG_LEVEL have to have a NEXT_PUBLIC_ prefix otherwise they only show up server side.

Seeing as this value is used in the init function, it probably would be better off passed into the init instead of assuming how consumers projects are set up.