Update messages api

[maxkahan]

This PR makes some updates to the Messages API:

• Adds the new Viber service message types file and video
• Adds the new WhatsApp type sticker and associated checks
• Adds new messages API tests

[codecov-commenter]

Codecov Report

:exclamation: No coverage uploaded for pull request base (main@4971eda). Click here to learn what that means. The diff coverage is 92.85%.

@@           Coverage Diff           @@
##             main     #251   +/-   ##
=======================================
  Coverage        ?   97.25%           
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  Files           ?       20           
  Lines           ?      728           
  Branches        ?        0           
=======================================
  Hits            ?      708           
  Misses          ?       20           
  Partials        ?        0           

Impacted Files	Coverage Δ
src/vonage/messages.py	98.11% <92.85%> (ø)

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