Update the version logic and tagging

[pawbhard]

Update the logic to determine if we need to tag the image
Also added a check to retag version if not present for pre-built image

Test for bash logic

bpawan@bpawan:~/workspace/code/psm-interop$ for val in kokoro kokoro-github-subscriber anonymous user123; do                                                                                                                                                                                              
      KOKORO_BUILD_INITIATOR="$val"                                                                                                                                                                                                                               
      if [[ "${KOKORO_BUILD_INITIATOR:-anonymous}" != kokoro* ]]; then                                                                                                                                                                                            
        echo "$val: DEV"                                                                                                                                                                                                                                          
      else                                                                                                                                                                                                                                                        
        echo "$val: OFFICIAL"                                                                                                                                                                                                                                     
      fi                                                                                                                                                                                                                                                          
    done   
kokoro: OFFICIAL
kokoro-github-subscriber: OFFICIAL
anonymous: DEV
user123: DEV
bpawan@bpawan:~/workspace/code/psm-interop$ 

[pawbhard]

Addressed comments , @sergiitk PTAL