Update swagger API specification (#1782)

# Summary

This PR drops the outdated former swagger.yaml/json and introduced
automatic API document generation from Go code.
The generated code is also used to generate documentation/markdown for
the community page,
as well as enable the Woodpecker server to serve a Swagger Web UI for
manual tinkering.

I did opt-in for gin-swagger, a middleware for the Gin framework, to
ease implementation and have a sophisticated output.
This middleware only produces Swagger v2 specs. AFAIK the newer OpenApi
3x tooling is not yet that mature,
so I guess that's fine for now.

## Implemenation notes

- former swagger.json files removed
- former // swagger godocs removed
- introduced new dependency gin-swagger, which uses godoc annotations on
top of Gin Handler functions.
- reworked Makefile to automatically generate Go code for the server
- introduce new dependency go-swagger, to generate Markdown for
documentation purposes
- add a Swagger Web UI, incl. capabilities for manual API exploration
- consider relative root paths in the implementation
- write documentation for all exposed API endpoints
- incl. API docs in the community website (auto-generated)
- provide developer documentation, for the Woodpecker authors
- no other existing logic/code was intentionally changed

---------

close #292

---------

Co-authored-by: qwerty287 <80460567+qwerty287@users.noreply.github.com>
Co-authored-by: 6543 <6543@obermui.de>

server/api/hook.go

@@ -35,22 +35,55 @@ import (
 
 var skipRe = regexp.MustCompile(`\[(?i:ci *skip|skip *ci)\]`)
 
+// GetQueueInfo
+//
+//	@Summary	Get pipeline queue information
+//	@Description	TODO: link the InfoT response object - this is blocked, until the `swaggo/swag` tool dependency is v1.18.12 or newer
+//	@Router		/queue/info [get]
+//	@Produce	json
+//	@Success	200	{object} map[string]string
+//	@Tags		Pipeline queues
+//	@Param		Authorization	header	string	true	"Insert your personal access token"	default(Bearer <personal access token>)
 func GetQueueInfo(c *gin.Context) {
 	c.IndentedJSON(http.StatusOK,
 		server.Config.Services.Queue.Info(c),
 	)
 }
 
+// PauseQueue
+//
+//	@Summary	Pause a pipeline queue
+//	@Router		/queue/pause [post]
+//	@Produce	plain
+//	@Success	200
+//	@Tags		Pipeline queues
+//	@Param		Authorization	header	string	true	"Insert your personal access token"	default(Bearer <personal access token>)
 func PauseQueue(c *gin.Context) {
 	server.Config.Services.Queue.Pause()
 	c.Status(http.StatusOK)
 }
 
+// ResumeQueue
+//
+//	@Summary	Resume a pipeline queue
+//	@Router		/queue/resume [post]
+//	@Produce	plain
+//	@Success	200
+//	@Tags		Pipeline queues
+//	@Param		Authorization	header	string	true	"Insert your personal access token"	default(Bearer <personal access token>)
 func ResumeQueue(c *gin.Context) {
 	server.Config.Services.Queue.Resume()
 	c.Status(http.StatusOK)
 }
 
+// BlockTilQueueHasRunningItem
+//
+//	@Summary	Block til pipeline queue has a running item
+//	@Router		/queue/norunningpipelines [get]
+//	@Produce	plain
+//	@Success	200
+//	@Tags		Pipeline queues
+//	@Param		Authorization	header	string	true	"Insert your personal access token"	default(Bearer <personal access token>)
 func BlockTilQueueHasRunningItem(c *gin.Context) {
 	for {
 		info := server.Config.Services.Queue.Info(c)
@@ -61,7 +94,14 @@ func BlockTilQueueHasRunningItem(c *gin.Context) {
 	c.Status(http.StatusOK)
 }
 
-// PostHook start a pipeline triggered by a forges post webhook
+// PostHook
+//
+//	@Summary	Incoming webhook from forge
+//	@Router		/hook [post]
+//	@Produce	plain
+//	@Success	200
+//	@Tags		System
+//	@Param		hook	body	object	true	"the webhook payload; forge is automatically detected"
 func PostHook(c *gin.Context) {
 	_store := store.FromContext(c)
 	forge := server.Config.Services.Forge