Add API to get/edit wiki (#17278)

* Add API to get/edit wiki

* Add swagger docs, various improvements

* fmt

* Fix lint and rm comment

* Add page parameter

* Add pagination to pages

* Add tests

* fmt

* Update func names

* Update error handling

* Update type name

* Fix lint

* Don't delete Home

* Update func name

* Update routers/api/v1/repo/wiki.go

Co-authored-by: delvh <dev.lh@web.de>

* Remove unnecessary check

* Fix lint

* Use English strings

* Update integrations/api_wiki_test.go

Co-authored-by: delvh <dev.lh@web.de>

* Update func and test names

* Remove unsed check and avoid duplicated error reports

* Improve error handling

* Return after error

* Document 404 error

* Update swagger

* Fix lint

* Apply suggestions from code review

Co-authored-by: delvh <dev.lh@web.de>

* Document file encoding

* fmt

* Apply suggestions

* Use convert

* Fix integration test

* simplify permissions

* unify duplicate key Title/Name

* improve types & return UTC timestamps

* improve types pt.2

- add WikiPageMetaData.LastCommit
- add WikiPageMetaData.HTMLURL
- replace WikiPageMetaData.Updated with .LastCommit.Committer.Created

also delete convert.ToWikiPage(), as it received too many arguments and
only had one callsite anyway. sorry for bad advice earlier 🙃

* WikiPage.Content is base64 encoded

* simplify error handling in wikiContentsByName()

* update swagger

* fix & DRY findWikiRepoCommit() error handling

ListWikiPages() previously wrote error twice when repo wiki didn't exist

* rename Content -> ContentBase64

* Fix test

* Fix tests

* Update var name

* suburl -> sub_url

Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Norwin <git@nroo.de>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/repo_wiki.go

@@ -0,0 +1,47 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package structs
+
+// WikiCommit page commit/revision
+type WikiCommit struct {
+	ID        string      `json:"sha"`
+	Author    *CommitUser `json:"author"`
+	Committer *CommitUser `json:"commiter"`
+	Message   string      `json:"message"`
+}
+
+// WikiPage a wiki page
+type WikiPage struct {
+	*WikiPageMetaData
+	// Page content, base64 encoded
+	ContentBase64 string `json:"content_base64"`
+	CommitCount   int64  `json:"commit_count"`
+	Sidebar       string `json:"sidebar"`
+	Footer        string `json:"footer"`
+}
+
+// WikiPageMetaData wiki page meta information
+type WikiPageMetaData struct {
+	Title      string      `json:"title"`
+	HTMLURL    string      `json:"html_url"`
+	SubURL     string      `json:"sub_url"`
+	LastCommit *WikiCommit `json:"last_commit"`
+}
+
+// CreateWikiPageOptions form for creating wiki
+type CreateWikiPageOptions struct {
+	// page title. leave empty to keep unchanged
+	Title string `json:"title"`
+	// content must be base64 encoded
+	ContentBase64 string `json:"content_base64"`
+	// optional commit message summarizing the change
+	Message string `json:"message"`
+}
+
+// WikiCommitList commit/revision list
+type WikiCommitList struct {
+	WikiCommits []*WikiCommit `json:"commits"`
+	Count       int64         `json:"count"`
+}