Display original author and URL information when showing migrated issues/comments

[mrsdizzie]

Per #7293

• Store original author name in issues + comments table
• Store original author user ID in issues + comments table
• Store original url in repo table
• Migrations for above

For Templates:

• Use original author name as display name for issue/PR author on issues/PR screen
• Use original author name as display name for all comments on issue/PR
• Use font awesome or similar to show icon of service it was migrated from (github only for now, soon to be gogs too)
• Link to original repo URL in comment headers
• Use different avatar than user who ran migration

Screenshots of old vs new behavior:

OLD	NEW

[lunny]

And if a user login with github OAuth2 and registered successfully, I think we can replace all the related issues and comments. So that he will have permission to edit that issues/comments.

[mrsdizzie]

And if a user login with github OAuth2 and registered successfully, I think we can replace all the related issues and comments. So that he will have permission to edit that issues/comments.

Sure, that can be another PR since this one will already have many changes. Storing the user ID in this PR should allow for that process later on. I will try to keep that in mind when changing the templates though so it will be easier going forward.

Right now it will check {{if .OriginalAuthor}}and show the original_authorstring instead of the Poster Display Name.

Maybe for a Gitea user who has registered with Github login then we can remove the original_authorand change the issue/comment to their Gitea user ID instead. Then it would just work with no new changes to the Template needed.

Or we could add an extra column and mark the issue as migrated to a different user and then check for that too.

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@fcda2d5). Click here to learn what that means.
The diff coverage is 9.21%.

@@            Coverage Diff            @@
##             master    #7352   +/-   ##
=========================================
  Coverage          ?   41.23%           
=========================================
  Files             ?      469           
  Lines             ?    63407           
  Branches          ?        0           
=========================================
  Hits              ?    26147           
  Misses            ?    33844           
  Partials          ?     3416

Impacted Files	Coverage Δ
models/issue.go	48.97% <ø> (ø)
modules/migrations/migrate.go	21.11% <ø> (ø)
models/migrations/migrations.go	1.32% <ø> (ø)
models/issue_comment.go	47.59% <ø> (ø)
modules/migrations/base/pullrequest.go	0% <ø> (ø)
models/migrations/v89.go	0% <0%> (ø)
modules/templates/helper.go	46.7% <0%> (ø)
modules/migrations/github.go	84.22% <100%> (ø)
modules/migrations/gitea.go	8.7% <2.85%> (ø)
models/repo.go	48.6% <25%> (ø)

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[mrsdizzie]

@lunny this is ready to start review.

I think the best way to assign comments in the future is to see if there is a match based on original_author_id and if so to change the poster_id to the local user and then delete original_author string but keep original_author_id. That way we keep the important information but the templates will act as normal if original_author is empty.

We can do this both as part of migration and afterwards if somebody signs up later and authenticates with their github account. Would be another PR but this one will start to store the information needed to make that happen.