Generate initrd & bootconfigs for Microdroid boot

Combine microdroid_ramdisk & microdroid_vendor_ramdisk images & this
will be microdroid_initrd in kernel_boot method. Also use the
initrd_bootconfig tool to attach bootconfig to it.

Also, collect all required bootconfigs. ABL, when verifying VBMeta, also
adds VBmeta digests & related configs to kernel command line. Without
ABL, we use bootconfig to send precomputed vbmeta digest. (Some of them
are computed using avbtool)

Test: Inspect the different build artifacts.
Bug: 240235424
Change-Id: I371c91db033a42bac6f0801a99490d18fc5dcdc1
diff --git a/apex/Android.bp b/apex/Android.bp
index 83985cc..a9fad55 100644
--- a/apex/Android.bp
+++ b/apex/Android.bp
@@ -63,6 +63,9 @@
     ],
     prebuilts: [
         "com.android.virt.init.rc",
+        "microdroid_initrd_app_debuggable",
+        "microdroid_initrd_full_debuggable",
+        "microdroid_initrd_normal",
         "microdroid.json",
         "microdroid_bootloader",
         "microdroid_bootloader.avbpubkey",