Replace megaease links to easegress-io

[xxx7xxxx]

No description provided.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.67%. Comparing base (49fda2d) to head (9ad1e09).

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Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1237      +/-   ##
==========================================
+ Coverage   79.62%   79.67%   +0.05%     
==========================================
  Files         152      152              
  Lines       17228    17228              
==========================================
+ Hits        13717    13726       +9     
+ Misses       2849     2841       -8     
+ Partials      662      661       -1     

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[xxx7xxxx]

Some integration tests failed with the message:

go: github.com/easegress-io/easegress/v2@upgrade (v2.7.1) requires github.com/easegress-io/easegress/[email protected]: parsing go.mod:
        module declares its path as: github.com/megaease/easegress/v2
                but was required as: github.com/easegress-io/easegress/v2
Error: exec 0x1034bd870 failed, exit status 1

So it's a deadlock-like situation, so we decided not to change the import paths currently since Golang module redirection works badly.