Prepared changes for releasing v3 (Project-MONAI#538)

* Prepared changes for releasing v3

Signed-off-by: M Q <mingmelvinq@nvidia.com>

* Bump the required version to 3.9

Signed-off-by: M Q <mingmelvinq@nvidia.com>

* Update Python version references to 3.9 in documentation and configuration files

- Updated .gitignore to include new input and test directories.
- Changed Python version from 3.8 to 3.9 in .readthedocs.yml, setup.cfg, and run script.
- Updated documentation to reflect the use of Python 3.9 in various tutorials.

Signed-off-by: M Q <mingmelvinq@nvidia.com>

---------

Signed-off-by: M Q <mingmelvinq@nvidia.com>
Signed-off-by: Simone Bendazzoli <simben@kth.se>

Author: MMelQin

docs/source/release_notes/v3.0.0.md

@@ -1,4 +1,4 @@
-# Version 3.0.0 (April 22nd, 2025)
+# Version 2.0.0 (April 24th, 2024)
 
 ## What's new in 3.0.0
 

requirements.txt

@@ -1,5 +1,6 @@
-holoscan~=2.0
+holoscan~=3.0
+holoscan-cli~=3.0
 numpy>=1.21.6
 colorama>=0.4.1
-tritonclient[all]
+tritonclient[all]>=2.53.0
 typeguard>=3.0.0