CMCL-0000: Add message banner for Cinemachine 2

[fatimah-mf-unity]

Purpose of this PR

Add message banner for status of Cinemachine 2 and 3 in Unity 6.5+.

JIRA: DOCG-9097

[cla-assistant-unity]

All committers have signed the CLA.

[u-pr]

💡 Harness Review

The shared deprecation notice is present on every published manual/API page in the package (with the navigation file correctly excluded), and the include target and relative references are consistent across the change.

_{Reviewed commit b26c7df}

_{🤖 Helpful? 👍/👎}

[codecov-github-com]

Codecov Report

All modified and coverable lines are covered by tests ✅

@@               Coverage Diff                @@
##           release/2.10    #1123      +/-   ##
================================================
- Coverage         25.17%   25.11%   -0.06%     
================================================
  Files               137      137              
  Lines             20216    20216              
================================================
- Hits               5089     5078      -11     
- Misses            15127    15138      +11     

Flag	Coverage Δ
cinemachine_MacOS_2022.3	?
cinemachine_MacOS_2022.3_project	?
cinemachine_MacOS_6000.0	?
cinemachine_MacOS_6000.0_project	?
cinemachine_MacOS_6000.3	?
cinemachine_MacOS_6000.3_project	?
cinemachine_MacOS_6000.4	?
cinemachine_MacOS_6000.4_project	?
cinemachine_MacOS_6000.5	?
cinemachine_MacOS_6000.5_project	?
cinemachine_MacOS_6000.6	?
cinemachine_MacOS_6000.6_project	?
cinemachine_Ubuntu_6000.0	?
cinemachine_Ubuntu_6000.0_project	?
cinemachine_Ubuntu_6000.3	?
cinemachine_Ubuntu_6000.3_project	?
cinemachine_Ubuntu_6000.4	?
cinemachine_Ubuntu_6000.4_project	?
cinemachine_Ubuntu_6000.5	?
cinemachine_Ubuntu_6000.5_project	?
cinemachine_Ubuntu_6000.6	?
cinemachine_Ubuntu_6000.6_project	?
cinemachine_Windows_2022.3	15.58% <ø> (ø)
cinemachine_Windows_2022.3_project	25.09% <ø> (-0.03%)	⬇️
cinemachine_Windows_6000.0	15.58% <ø> (ø)
cinemachine_Windows_6000.0_project	25.07% <ø> (ø)
cinemachine_Windows_6000.3	15.58% <ø> (ø)
cinemachine_Windows_6000.3_project	25.07% <ø> (ø)
cinemachine_Windows_6000.4	15.58% <ø> (ø)
cinemachine_Windows_6000.4_project	25.07% <ø> (ø)
cinemachine_Windows_6000.5	15.58% <ø> (ø)
cinemachine_Windows_6000.5_project	25.07% <ø> (ø)
cinemachine_Windows_6000.6	?
cinemachine_Windows_6000.6_project	25.09% <ø> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

see 3 files with indirect coverage changes

ℹ️ Need help interpreting these results?

[glabute]

This sounds like Cinemachine is being removed. You need to say where they ARE available, not just where they aren't available.

[sebastienduverne]

I hope it's better like this. I also added a link to the CM2 > CM3 upgrade guide. I intentionally made the upgrade thing only a soft recommendation, as it can be a pain and it's not mandatory.

Suggested change

> Cinemachine 2 is deprecated in Unity 6.5 and later. In Unity 6.6 and later, Cinemachine 2 and Cinemachine 3 aren't available in the Package Manager, and the version of Cinemachine matches your Unity Editor version.

> Cinemachine 2 is deprecated in Unity 6.5 and later. In Unity 6.6 and later, Cinemachine 2 and Cinemachine 3 aren't available in the Package Manager. You can use the Cinemachine version that matches your Unity Editor version instead. If you decide to upgrade your project from Cinemachine 2 to a later version, refer to [Upgrade a Project from Cinemachine 2.x](https://docs.unity3d.com/Packages/com.unity.cinemachine@3.1/manual/CinemachineUpgradeFrom2.html).

[glabute]

It still feels a little destabilizing. How can I use a Cinemachine version if Cinemachine is no longer available in the package manager? Where do I get it from?