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This PR drops the outdated former swagger.yaml/json and introduced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

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

server/api/org.go

@@ -24,7 +24,15 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// GetOrgPermissions returns the permissions of the current user in the given organization.
+// GetOrgPermissions
+//
+//	@Summary	Get the permissions of the current user in the given organization
+//	@Router		/orgs/{owner}/permissions [get]
+//	@Produce	json
+//	@Success	200	{array}	OrgPerm
+//	@Tags		Organization permissions
+//	@Param		Authorization	header	string	true	"Insert your personal access token"	default(Bearer <personal access token>)
+//	@Param		owner			path	string	true	"the owner's name"
 func GetOrgPermissions(c *gin.Context) {
 	var (
 		err   error