fix: Specify download .tgz extension

[simster7]

Fixes: #2163 by adding the Content-Disposition header with the desired file extension.

Thanks @ddseapy for reporting this bug.

[codecov]

Codecov Report

Merging #2164 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master   #2164      +/-   ##
=========================================
+ Coverage    11.7%   11.7%   +<.01%     
=========================================
  Files          51      51              
  Lines       26329   26321       -8     
=========================================
  Hits         3081    3081              
+ Misses      22853   22845       -8     
  Partials      395     395

Impacted Files	Coverage Δ
persist/sqldb/migrate.go	0% <0%> (ø)	⬆️

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