Caps the apache-airflow version to 2.2.x. (tensorflow#4890)

There is a conflicting dependency in apache-airflow 2.3.0
- apache-airflow 1.23.0 -> rich '12.3.0' -> typing-extensions (>=4.0.0,<5.0); python_version < "3.9"
- kfp 1.8.12 -> typing-extensions (<4,>=3.7.4); python_version < "3.9"

This issue will be resolved when kfp releases a new version because kfp already changed the cap in kubeflow/pipelines#7632.

PiperOrigin-RevId: 446236647
(cherry picked from commit 2df92b3)

Co-authored-by: jiyongjung <jiyongjung@google.com>

Update 1.8.0 in version.py (tensorflow#4886)

Update 1.8.0 in version.py and RELEASE.md (tensorflow#4876)

* Update 1.8.0 in version.py and RELEASE.md

* Updated version.py for TFX 1.8.0-rc0

Update 1.5.1 in version.py (tensorflow#4851)

Update 1.7.1 in version.py (tensorflow#4790)

TFX 1.6.2 Release (tensorflow#4785)

Update version.py for TFX 1.7.0 Release (tensorflow#4747)

Fix MLMD and Struct2Tensor versions in dependencies.py to match 1.7.0…

…/0.38.0 release release train. (tensorflow#4731)

PiperOrigin-RevId: 433639728

Co-authored-by: tfx-team <tensorflow-extended-nonhuman@googlegroups.com>

Update 1.6.1 in version.py (tensorflow#4656)

Co-authored-by: jiyongjung <jiyongjung@google.com>

Update version.py for TFX 1.6.0 Release (tensorflow#4631)