Update ANDROID_APP_VERSION to be dynamic based on OPENEDX_COMMON_VERSION

[hamza-56]

This PR updates the logic for setting the ANDROID_APP_VERSION in the Dockerfile. The new logic uses a conditional statement to determine the value based on the OPENEDX_COMMON_VERSION variable.

For the nightly build, set ANDROID_APP_VERSION to main.
For master and redwood branches, set ANDROID_APP_VERSION to the value of OPENEDX_COMMON_VERSION.

[regisb]

This change should be made to the master branch, not the nightly branch. Also, please add a changelog entry: https://docs.tutor.overhang.io/tutor.html#contributing

EDIT: it's OK to merge in nightly, as long as the redwood branch is rebased on top of nightly.

[DawoudSheraz]

This change should be made to the master branch, not the nightly branch. Also, please add a changelog entry: https://docs.tutor.overhang.io/tutor.html#contributing

This is for the new android app, and those initial changes were merged to nightly.

My comment was not relevant.

[regisb]

lgtm!