Added signed URLs

[getvictor]

For #24869

This subtask contains code to sign the CloudFront software installer and bootstrap package URL using AWS SDK URL signer.
It works with the current bootstrap package delivery. For software installers, fleetd will need to be modified to take advantage of this URL in a future subtask (which will also include updated API contributor docs).

My article on signed URLs, for context: https://victoronsoftware.com/posts/cloudfront-signed-urls/

Checklist for submitter

• Added/updated automated tests
• Manual QA for all new/changed functionality

[codecov]

Codecov Report

Attention: Patch coverage is 64.70588% with 66 lines in your changes missing coverage. Please review.

Project coverage is 63.84%. Comparing base (7e1a808) to head (9bc0bc9).
Report is 13 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/fleet/serve.go	0.00%	16 Missing ⚠️
server/worker/apple_mdm.go	62.50%	10 Missing and 2 partials ⚠️
server/datastore/s3/common_file_store.go	35.71%	6 Missing and 3 partials ⚠️
server/mdm/cryptoutil/cryptoutil.go	78.37%	6 Missing and 2 partials ⚠️
server/config/config.go	63.15%	6 Missing and 1 partial ⚠️
cmd/fleet/cron.go	0.00%	4 Missing ⚠️
ee/server/service/software_installers.go	91.89%	2 Missing and 1 partial ⚠️
server/datastore/filesystem/software_installer.go	0.00%	2 Missing ⚠️
server/fleet/errors.go	0.00%	2 Missing ⚠️
server/fleet/software_installer.go	0.00%	2 Missing ⚠️
... and 1 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25197      +/-   ##
==========================================
- Coverage   63.85%   63.84%   -0.01%     
==========================================
  Files        1617     1617              
  Lines      153841   153965     +124     
  Branches     4032     4032              
==========================================
+ Hits        98231    98304      +73     
- Misses      47794    47838      +44     
- Partials     7816     7823       +7     

Flag	Coverage Δ
backend	64.72% <64.70%> (-0.01%)	⬇️

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[gillespi314]

Looks great. Thanks for the link to the article!