feat: default http client timeout override

[or-shachar]

Checklist

=========

• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ x I have checked for similar issues and haven't found anything relevant.
• [x] This is not a security issue (which should be reported here: https://circleci.com/security/)
• [x] I have read Contribution Guidelines.

Changes

• Fixed #1012
• Allows using HTTP_TIMEOUT env variable:

  export HTTP_TIMEOUT=30s
  circleci config validate config.yml

Considerations

• 10 seconds should definitely be enough for the API server to respond
• This override feature is only for cases where there is some temporal misbehavior.

[or-shachar]

@loderunner - I've changed the name of the env variable to CIRCLECI_CLI_TIMEOUT - feel free to squash/merge + introduce a new PR with changes to the GQL client as well 🙏

[abdelDriowya]

Thanks @or-shachar for your contribution, I will add timeout to graphql client and we will merge the pr after that