Add option for installing from release archive

[andrjohns]

Submission Checklist

• Run unit tests
• Declare copyright holder and agree to license (see below)

Summary

Closes #865 by adding the option to install cmdstan from a downloaded release archive:

install_cmdstan(release_file = "./cmdstan-2.33.1.tar.gz")

Copyright and Licensing

Please list the copyright holder for the work you are submitting
(this will be you or your assignee, such as a university or company):
Andrew Johnson

By submitting this pull request, the copyright holder is agreeing to
license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[codecov-commenter]

Codecov Report

Merging #866 (73157b4) into master (ede72e3) will decrease coverage by 0.03%.
The diff coverage is 88.88%.

❗ Current head 73157b4 differs from pull request most recent head 94508ef. Consider uploading reports for the commit 94508ef to get more accurate results

@@            Coverage Diff             @@
##           master     #866      +/-   ##
==========================================
- Coverage   88.32%   88.30%   -0.03%     
==========================================
  Files          12       12              
  Lines        4370     4377       +7     
==========================================
+ Hits         3860     3865       +5     
- Misses        510      512       +2     

Files	Coverage Δ
R/install.R	63.14% <88.88%> (+0.12%)	⬆️

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[jgabry]

Thanks!