Bundle ProGuard rules in AAR

[Goooler]

Refs https://square.github.io/okhttp/features/r8_proguard/.

OLD: showkase-release-before.aar
NEW: showkase-release-after.aar

 AAR      │ old       │ new       │ diff
──────────┼───────────┼───────────┼───────
      jar │ 327.8 KiB │ 327.8 KiB │   0 B
 manifest │     710 B │     710 B │   0 B
      res │     920 B │     920 B │   0 B
    other │     553 B │     633 B │ +80 B
──────────┼───────────┼───────────┼───────
    total │   330 KiB │   330 KiB │ +80 B

 JAR     │ old │ new │ diff
─────────┼─────┼─────┼───────────
 classes │ 182 │ 182 │ 0 (+0 -0)
 methods │ 987 │ 987 │ 0 (+0 -0)
  fields │ 469 │ 469 │ 0 (+0 -0)

=================
====   AAR   ====
=================

 size │ diff  │ path
──────┼───────┼────────────────
 81 B │ +80 B │ ∆ proguard.txt
──────┼───────┼────────────────
 81 B │ +80 B │ (total)

[vinaygaba]

Thanks for your change - this is a lot cleaner and easier for the users of the library