Signing without testkey and debug key

[s1204IT]

• Sign overlay apks with a throwaway key
  • Signing of com.mtg.gmsoverlay and com.mtg.gmssettingsprovideroverlay uses a publicly known/shared private key
  • https://gitlab.com/LineageOS/issues/android/-/issues/5230
• Use apksigner for signing overlay apks

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With this change, we will also change the file used for that signature to be uploaded.
Actually, it is not necessary, but done just in case.