Fix sdkmanager URL and path

[Sugihiru]

The Flutter image is currently broken due to the changes in the Android side from sdk-tools to cmdline-tools, which is known to be a problem Flutter side with flutter doctor. The following problem occurs when using the current sdk-tools :

Step #0: Step 23/28 : RUN yes "y" | flutter doctor --android-licenses
Step #0:  ---> Running in 1b6620ba9317
Step #0: [91mAndroid sdkmanager not found. Update to the latest Android SDK and ensure that the cmdline-tools are installed to resolve this.
Step #0: The command '/bin/sh -c yes "y" | flutter doctor --android-licenses' returned a non-zero code: 1
Finished Step #0
ERROR

This PR uses cmdline-tools and updates the paths accordingly

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[Sugihiru]

@googlebot I fixed it.

[Sese-Schneider]

@amcooper this is cruicial to fix the flutter cloud builder. I came across the same issue and luckily this PR fixes it.

[CriPstian]

I also confirm this PR fixes the cloud builder. How could we get this into the main repo?

[amcooper]

@ronanww ?