Added warning for special URL sensitive characters for appId

[ssafayet]

If we use reserved and unwise character in context of a URI/URL inside an Application ID, it can create issues in many cases such as:

1. The rendered URL for a password reset, email verification won't work as it fails to be rendered in the actual application id resulted in unauthorized.
2. The file download will be an issue as parse uses application id in the URL too.

So I included a warning message for some reserved character in the context of URL which can cause problems where application id is included in a URL.

[dplewis]

Just a comment from me. Can you add a test case as well?

[codecov]

Codecov Report

Merging #6159 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6159      +/-   ##
==========================================
- Coverage   93.78%   93.77%   -0.01%     
==========================================
  Files         166      166              
  Lines       11271    11275       +4     
==========================================
+ Hits        10570    10573       +3     
- Misses        701      702       +1

Impacted Files	Coverage Δ
src/ParseServer.js	97.59% <100%> (+0.05%)	⬆️
...dapters/Storage/Postgres/PostgresStorageAdapter.js	97.01% <0%> (-0.09%)	⬇️
src/RestWrite.js	93.72% <0%> (ø)	⬆️

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[dplewis]

LGTM! @saimoomsafayet Are there other characters you can think of?