appservice: support binding wildcard certificates

[yugangw-msft]

fix #2561
(per standard, wildcard only covers one level of subdomains)

[codecov-io]

Codecov Report

Merging #2625 into master will increase coverage by 0.03%.
The diff coverage is 91.3%.

@@            Coverage Diff             @@
##           master    #2625      +/-   ##
==========================================
+ Coverage   71.95%   71.99%   +0.03%     
==========================================
  Files         375      375              
  Lines       20602    20612      +10     
  Branches     3012     3017       +5     
==========================================
+ Hits        14825    14839      +14     
- Misses       4846     4848       +2     
+ Partials      931      925       -6

Impacted Files	Coverage Δ
...ice/azure/cli/command_modules/appservice/custom.py	74.11% <91.3%> (+1.18%)	⬆️
...-cli-role/azure/cli/command_modules/role/custom.py	17.89% <0%> (ø)	⬆️
...dback/azure/cli/command_modules/feedback/custom.py	34.69% <0%> (ø)	⬆️
src/azure-cli-core/azure/cli/core/_util.py	66.66% <0%> (ø)	⬆️

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