feat(docs): `cache` middleware documentation

[rustatian]

Reason for This PR

• RR 2.7 release polishing
• closes: #201

Description of Changes

• Add cache docs
• Simplify cache send response operation

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

[Author TODO: Meet these criteria.] [Reviewer TODO: Verify that these criteria are met. Request changes if not]

• [x] All commits in this PR are signed (git commit -s).
• [x] The reason for this PR is clearly provided (issue no. or explanation).
• [x] The description of changes is clear and encompassing.
• [x] Any required documentation changes (code and docs) are included in this PR.
• [x] Any user-facing changes are mentioned in CHANGELOG.md.
• [x] All added/changed functionality is tested.

[codecov[bot]]

Codecov Report

Merging #200 (9c6cb04) into master (c9ea93f) will increase coverage by 0.07%. The diff coverage is 64.70%.

@@            Coverage Diff             @@
##           master     #200      +/-   ##
==========================================
+ Coverage   68.40%   68.47%   +0.07%     
==========================================
  Files         141      141              
  Lines       10827    10824       -3     
==========================================
+ Hits         7406     7412       +6     
+ Misses       2647     2641       -6     
+ Partials      774      771       -3     

Impacted Files	Coverage Δ
http/middleware/cache/cache.go	48.57% <0.00%> (-2.95%)	:arrow_down:
http/middleware/cache/get.go	69.44% <73.33%> (+3.21%)	:arrow_up:
amqp/amqpjobs/item.go	73.28% <0.00%> (-1.37%)	:arrow_down:
sqs/sqsjobs/item.go	67.10% <0.00%> (+1.31%)	:arrow_up:
jobs/listener.go	56.70% <0.00%> (+4.12%)	:arrow_up:
jobs/protocol/handler.go	82.08% <0.00%> (+4.47%)	:arrow_up:

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