fix: CMS content type check

[JeyJeyGao]

What this PR does / why we need it:
Previously, the CMS package was generically designed for RFC 5652. However, since the CMS package will not be exported and we only need to care about RFC 3161, we can restrict the CMS content type to TSTInfo (id-ct-TSTInfo) to fail fast.

Which issue(s) this PR resolves (optional, in resolves #<issue number>(, resolves #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Resolves #33

Please check the following list:

• Does the affected code have corresponding tests, e.g. unit test?
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have an appropriate license header?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.52%. Comparing base (df25ef8) to head (50a72b3).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #35      +/-   ##
==========================================
- Coverage   95.24%   94.52%   -0.72%     
==========================================
  Files          19       19              
  Lines         736      932     +196     
==========================================
+ Hits          701      881     +180     
- Misses         18       34      +16     
  Partials       17       17              

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[Two-Hearts]

LGTM

[shizhMSFT]

LGTM

[priteshbandi]

LGTM