adding decompress gzipped request middleware

[arun0009]

Adding decompress middleware that decompresses request if content-encoding is set to "gzip". We send in large amounts of data and we want to compress data on the network and decompress it in API. This is trivial for any API that ingests a large amount of payload. Also addresses one of the issues logged on echo #986.

Added tests as well to cover most of the scenarios. Can you please review @lammel

P.S Build was failing as github actions deprecated passing env variables, updated workflows/echo.yaml to fix this issue. More details here https://github.blog/changelog/2020-10-01-github-actions-deprecating-set-env-and-add-path-commands/

[codecov]

Codecov Report

Merging #1687 (b47042f) into master (7a90304) will increase coverage by 0.10%.
The diff coverage is 94.73%.

@@            Coverage Diff             @@
##           master    #1687      +/-   ##
==========================================
+ Coverage   84.35%   84.45%   +0.10%     
==========================================
  Files          28       29       +1     
  Lines        1911     1930      +19     
==========================================
+ Hits         1612     1630      +18     
- Misses        189      190       +1     
  Partials      110      110              

Impacted Files	Coverage Δ
middleware/decompress.go	94.73% <94.73%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7a90304...b47042f. Read the comment docs.

[lammel]

Looking good!

Would you mind adding a PR for this middleware with an example for the documentation in echox project?
That would definitely be helpful for all those backend REST API wrestlers our there having to transfer bigger payloads.

As the PR is already cleanup up, tests added and no breaking changes, will merge.

Thanks @arun0009 !