Add easyMDE(simpleMDE) support for release content editor

[a1012112796]

As title

example view:

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[codecov-io]

Codecov Report

Merging #14744 (dc6d29a) into master (487f2ee) will increase coverage by 0.01%.
The diff coverage is 42.26%.

@@            Coverage Diff             @@
##           master   #14744      +/-   ##
==========================================
+ Coverage   42.21%   42.23%   +0.01%     
==========================================
  Files         767      771       +4     
  Lines       81624    82086     +462     
==========================================
+ Hits        34458    34666     +208     
- Misses      41531    41779     +248     
- Partials     5635     5641       +6     

Impacted Files	Coverage Δ
models/action.go	48.52% <0.00%> (-2.42%)	⬇️
models/migrations/migrations.go	2.59% <ø> (ø)
models/migrations/v166.go	0.00% <0.00%> (ø)
models/migrations/v172.go	0.00% <0.00%> (ø)
models/migrations/v173.go	0.00% <0.00%> (ø)
models/session.go	0.00% <0.00%> (ø)
models/user.go	53.05% <ø> (+0.38%)	⬆️
modules/context/context.go	58.05% <0.00%> (-0.45%)	⬇️
modules/indexer/code/elastic_search.go	1.72% <0.00%> (-0.02%)	⬇️
modules/migrations/github.go	77.77% <0.00%> (-1.99%)	⬇️
... and 64 more

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[zeripath]

Have you tested the preview page and are happy that relative links from it match when they are finally rendered?

[a1012112796]

Have you tested the preview page and are happy that relative links from it match when they are finally rendered?

yes, see #14744 (comment)

[zeripath]

I was meaning links like:

[README.md]

[a1012112796]

I was meaning links like:

[README.md]

It's a link?

[zeripath]

Sorry [README.md](README.md)

[a1012112796]

Sorry [README.md](README.md)

the results is same:

[6543]

🚀