Improve protected branch setting page (#24379)

Main changes:

1. Change html structure of protected branch page, use [`grouped
fields`](https://fomantic-ui.com/collections/form.html#grouped-fields)
instead of `fields` for better margin, and wrap `grouped fields` around
related `field`s, remove unnecessary `<div id="protection_box"
class="fields">` outer div

2. Changed some order of field to make them more categorized, used `ui
dividing header` for categorization and fine tune css.

Before:

<img width="1907" alt="Screen Shot 2023-04-27 at 14 56 19"
src="https://user-images.githubusercontent.com/17645053/234783731-bce8a7ce-dfc9-4d47-a3a8-b962ebea9467.png">
<img width="1849" alt="Screen Shot 2023-04-27 at 14 56 30"
src="https://user-images.githubusercontent.com/17645053/234783740-c47d314e-5e2d-4854-98fd-c88f85ef3584.png">
<img width="1872" alt="Screen Shot 2023-04-27 at 14 56 36"
src="https://user-images.githubusercontent.com/17645053/234783745-18e35a75-07e8-451d-b001-f9bcf16fcab5.png">

After:


https://user-images.githubusercontent.com/17645053/235114568-da010aad-7654-4410-ab8c-5d0fce7edadb.mov



3. Changed "Enable Merge Whitelist" to radio checkbox, and added "Enable
Merge" radio checkbox, which are exclusive

Before:

<img width="926" alt="Screen Shot 2023-04-28 at 13 08 29"
src="https://user-images.githubusercontent.com/17645053/235059233-75790f7a-e5ea-4e1c-82c6-509fef8b84b3.png">

After:

<img width="942" alt="Screen Shot 2023-04-28 at 13 09 28"
src="https://user-images.githubusercontent.com/17645053/235059367-852d1f61-8407-4126-8c79-315b9c1ffada.png">


4. Add a link to set default branch on branch list page (with reference
to github)


https://user-images.githubusercontent.com/17645053/234787404-61c1c7b6-aabf-429f-a109-5b690e4e0b5a.mov

5. Removed dead codes.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

options/locale/locale_en-US.ini

@@ -1901,6 +1901,7 @@ settings.sync_mirror = Synchronize Now
 settings.mirror_sync_in_progress = Mirror synchronization is in progress. Check back in a minute.
 settings.site = Website
 settings.update_settings = Update Settings
+settings.branches.switch_default_branch = Switch Default Branch
 settings.branches.update_default_branch = Update Default Branch
 settings.branches.add_new_rule = Add New Rule
 settings.advanced_settings = Advanced Settings
@@ -2096,6 +2097,8 @@ settings.event_pull_request_review = Pull Request Reviewed
 settings.event_pull_request_review_desc = Pull request approved, rejected, or review comment.
 settings.event_pull_request_sync = Pull Request Synchronized
 settings.event_pull_request_sync_desc = Pull request synchronized.
+settings.event_pull_request_approvals = Pull Request Approvals
+settings.event_pull_request_merge = Pull Request Merge
 settings.event_package = Package
 settings.event_package_desc = Package created or deleted in a repository.
 settings.branch_filter = Branch filter
@@ -2151,13 +2154,15 @@ settings.protected_branch.delete_rule = Delete Rule
 settings.protected_branch_can_push = Allow push?
 settings.protected_branch_can_push_yes = You can push
 settings.protected_branch_can_push_no = You cannot push
-settings.branch_protection = Branch Protection for Branch '<b>%s</b>'
+settings.branch_protection = Branch Protection Rules for Branch '<b>%s</b>'
 settings.protect_this_branch = Enable Branch Protection
 settings.protect_this_branch_desc = Prevents deletion and restricts Git pushing and merging to the branch.
 settings.protect_disable_push = Disable Push
 settings.protect_disable_push_desc = No pushing will be allowed to this branch.
 settings.protect_enable_push = Enable Push
 settings.protect_enable_push_desc = Anyone with write access will be allowed to push to this branch (but not force push).
+settings.protect_enable_merge = Enable Merge
+settings.protect_enable_merge_desc = Anyone with write access will be allowed to merge the pull requests into this branch.
 settings.protect_whitelist_committers = Whitelist Restricted Push
 settings.protect_whitelist_committers_desc = Only whitelisted users or teams will be allowed to push to this branch (but not force push).
 settings.protect_whitelist_deploy_keys = Whitelist deploy keys with write access to push.
@@ -2183,6 +2188,7 @@ settings.dismiss_stale_approvals_desc = When new commits that change the content
 settings.require_signed_commits = Require Signed Commits
 settings.require_signed_commits_desc = Reject pushes to this branch if they are unsigned or unverifiable.
 settings.protect_branch_name_pattern = Protected Branch Name Pattern
+settings.protect_patterns = Patterns
 settings.protect_protected_file_patterns = "Protected file patterns (separated using semicolon ';'):"
 settings.protect_protected_file_patterns_desc = "Protected files are not allowed to be changed directly even if user has rights to add, edit, or delete files in this branch. Multiple patterns can be separated using semicolon (';'). See <a href='https://pkg.go.dev/github.com/gobwas/glob#Compile'>github.com/gobwas/glob</a> documentation for pattern syntax. Examples: <code>.drone.yml</code>, <code>/docs/**/*.txt</code>."
 settings.protect_unprotected_file_patterns = "Unprotected file patterns (separated using semicolon ';'):"