add access tier methods

[samtkaplan]

alternative for #88

[codecov]

Codecov Report

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.75%. Comparing base (592c1dc) to head (616f29e).

Files with missing lines	Patch %	Lines
src/AzStorage.jl	81.25%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #90      +/-   ##
==========================================
- Coverage   83.86%   83.75%   -0.11%     
==========================================
  Files           1        1              
  Lines         533      548      +15     
==========================================
+ Hits          447      459      +12     
- Misses         86       89       +3     

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[mtorralba24-chev]

Looks good to me!

I added a small note in the descriptions of tier!().

If an archived blob is being "rehydrated" to a higher tier while someone calls the tier!(), the request will return a 409, and an exception will be thrown (after too many retries). A user might see an exception and think something is wrong, but a 409 is expected behavior of the tier api, and maybe just needs to wait it out.