DEVX-6999: Messages API Updates

[superchilled]

Updates Messaging functionality to:

• Add video and file types for Viber
• Add sticker type for WhatsApp

[codecov-commenter]

Codecov Report

Merging #260 (13c2b53) into dev (1e33d4c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 13c2b53 differs from pull request most recent head f92e1f8. Consider uploading reports for the commit f92e1f8 to get more accurate results

@@           Coverage Diff           @@
##              dev     #260   +/-   ##
=======================================
  Coverage   97.73%   97.74%           
=======================================
  Files          71       71           
  Lines        1457     1463    +6     
=======================================
+ Hits         1424     1430    +6     
  Misses         33       33           

Impacted Files	Coverage Δ
lib/vonage/messaging/channels/viber.rb	100.00% <100.00%> (ø)
lib/vonage/messaging/channels/whats_app.rb	100.00% <100.00%> (ø)

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