Add PR pipeline list (#1641)

Instead of viewing PR pipelines in the branches lists, add a separate
list for them. The API endpoint for PRs supports pagination (thus I
added a lot of pagination-related stuff), the UI doesn't yet though.


![wp](https://user-images.githubusercontent.com/80460567/226099133-bb4935d6-c357-4d73-8465-9157e25c0d82.png)

Closes #1619 

Extends this part of #1640

---------

Co-authored-by: Anbraten <anton@ju60.de>

server/router/middleware/session/pagination.go

@@ -0,0 +1,28 @@
+package session
+
+import (
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+	"github.com/woodpecker-ci/woodpecker/server/model"
+)
+
+const (
+	defaultPage    = 1
+	defaultPerPage = 25
+)
+
+func Pagination(c *gin.Context) *model.PaginationData {
+	page, err := strconv.ParseInt(c.Param("page"), 10, 64)
+	if err != nil {
+		page = defaultPage
+	}
+	perPage, err := strconv.ParseInt(c.Param("perPage"), 10, 64)
+	if err != nil {
+		perPage = defaultPerPage
+	}
+	return &model.PaginationData{
+		Page:    page,
+		PerPage: perPage,
+	}
+}