Bump Flint version to 0.7.0

[ykmr1224]

Description

• Bump Flint version to 0.7.0

Related Issues

n/a (This is for starting release process for v0.6.0)

Check List

• [ ] Updated documentation (docs/ppl-lang/README.md)
• [ ] Implemented unit tests
• [ ] Implemented tests for combination with other commands
• [ ] New added source code should include a copyright header
• [x] Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license. For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[noCharger]

Let's make sure this pr merged first before any backport to 0.6