[feat] sse client support method and body configure

[vegetablechicken233]

Make HTTP Method configurable and add corresponding test functions.
It should be noted that to ensure backward compatibility, the "method" field does not perform empty validation, but is set to "GET" by default (to align with the old version).
In addition, type of "body" field is temporarily set to "io.Reader" (it seems a bit too early to add support for "any"~

Separated from PR #985

[jeevatkm]

@vegetablechicken233 Thanks for creating a new PR. Just one minor comment on godoc. Once fixed, I will get it merged.

[jeevatkm]

@vegetablechicken233 This good example requires a correction based on method input type. Also, it has a syntax issue: , is present near the closing curve bracket.

es.SetBody(strings.NewReader(`{"test":"put_data"}`))

[vegetablechicken233]

@jeevatkm already fix it

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.82%. Comparing base (981bb3f) to head (02cc4dd).
Report is 1 commits behind head on v3.

Additional details and impacted files

@@           Coverage Diff           @@
##               v3     #988   +/-   ##
=======================================
  Coverage   99.81%   99.82%           
=======================================
  Files          18       18           
  Lines        3885     3896   +11     
=======================================
+ Hits         3878     3889   +11     
  Misses          5        5           
  Partials        2        2           

Flag	Coverage Δ
unittests	99.82% <100.00%> (+<0.01%)	⬆️

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[jeevatkm]

Thanks for the updates.