Add Gitea Profile Readmes (#23260)

Implements displaying a README.md file present in a users ```.profile```
repository on the users profile page. If no such repository/file is
present, the user's profile page remains unchanged.

Example of user with ```.profile/README.md```

![image](https://user-images.githubusercontent.com/34464552/222757202-5d53ac62-60d9-432f-b9e3-2537ffa91041.png)

Example of user without ```.profile/README.md```

![image](https://user-images.githubusercontent.com/34464552/222759972-576e058b-acd4-47ac-be33-38a7cb58cc81.png)

This pull request closes the feature request in #12233 

Special thanks to @techknowlogick for the help in the Gitea discord!

---------

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: Yarden Shoham <hrsi88@gmail.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: yp05327 <576951401@qq.com>
Co-authored-by: Yarden Shoham <git@yardenshoham.com>

routers/web/shared/user/header.go

@@ -4,7 +4,9 @@
 package user
 
 import (
+	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/modules/context"
+	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/setting"
 )
 
@@ -13,4 +15,24 @@ func RenderUserHeader(ctx *context.Context) {
 	ctx.Data["IsPackageEnabled"] = setting.Packages.Enabled
 	ctx.Data["IsRepoIndexerEnabled"] = setting.Indexer.RepoIndexerEnabled
 	ctx.Data["ContextUser"] = ctx.ContextUser
+	tab := ctx.FormString("tab")
+	ctx.Data["TabName"] = tab
+	repo, err := repo_model.GetRepositoryByName(ctx.ContextUser.ID, ".profile")
+	if err == nil && !repo.IsEmpty {
+		gitRepo, err := git.OpenRepository(ctx, repo.RepoPath())
+		if err != nil {
+			ctx.ServerError("OpenRepository", err)
+			return
+		}
+		defer gitRepo.Close()
+		commit, err := gitRepo.GetBranchCommit(repo.DefaultBranch)
+		if err != nil {
+			ctx.ServerError("GetBranchCommit", err)
+			return
+		}
+		blob, err := commit.GetBlobByPath("README.md")
+		if err == nil && blob != nil {
+			ctx.Data["ProfileReadme"] = true
+		}
+	}
 }