REST API: Add compression to REST API (#1390)

[Eric-Warehime]

This merges the changes from #1390 into the hotfix branch. I've done this via a separate PR because it was easier than changing the base of the previous PR and resolving a bunch of merge conflicts.

Here's a copy of the description of the other PR for reference:

Summary

In order to more easily support returning responses for blocks containing large numbers of transactions, we're adding gzip compression as an available response content encoding.

In order to have a response gzip'd (limited in this PR only to the /v2/block/ endpoint) clients can provide the header:

Accept-Encoding: gzip

For example, in the go-algorand-sdk, you could use the following code to retrieve a compressed block:

client.LookupBlock(rnd).Do(ctx, &common.Header{Key: "Accept-Encoding", Value: "gzip"})

See https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Accept-Encoding for more details on the Accept-Encoding header.

Test Plan

Added tests for compressed responses from /v2/blocks.

[codecov]

Codecov Report

Merging #1394 (4804caf) into hotfix/2.15.1 (300b69f) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@                Coverage Diff                @@
##           hotfix/2.15.1    #1394      +/-   ##
=================================================
+ Coverage          65.02%   65.03%   +0.01%     
=================================================
  Files                 52       52              
  Lines               8311     8315       +4     
=================================================
+ Hits                5404     5408       +4     
  Misses              2433     2433              
  Partials             474      474              

Impacted Files	Coverage Δ
api/server.go	63.75% <100.00%> (+1.90%)	⬆️

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