feat(pprof): add profiling route handler to debug runtime (#1818)

(cherry picked from commit 56ddb70f624e7070ad0d3531d498675f9f82c664)

Signed-off-by: Alex Stan <alexandrustan96@yahoo.ro>
Signed-off-by: Andrei Aaron <aaaron@luxoft.com>
Co-authored-by: Alex Stan <alexandrustan96@yahoo.ro>

pkg/debug/pprof/pprof.md

@@ -0,0 +1,33 @@
+# Profiling in Zot
+
+This project gives the user the posibility to debug and profile the runtime to find relevant data such as CPU intensive function calls. An in-depth article on profiling in Go can be found [here](https://go.dev/blog/pprof).
+
+A call to http://localhost:8080/v2/_zot/pprof/ would list the following available profiles, wrapped in an HTML file, with count values prior to change due to the runtime:
+
+```
+Types of profiles available:
+Count	Profile
+95	allocs
+0	block
+0	cmdline
+11	goroutine
+95	heap
+0	mutex
+0	profile
+13	threadcreate
+0	trace
+full goroutine stack dump
+```
+
+For example, the following can be used to gather the cpu profile for the amount of seconds specified as a query parameter, and then the results are stored in `cpu.prof` file:
+```
+curl -sK -v http://localhost:8080/v2/_zot/pprof/profile?seconds=30 > cpu.prof
+```
+
+Then, the user can use the `go tool pprof` to analyze the information generated previously in `cpu.prof`. The following command boots up an http server with a GUI and multiple charts that represent the data.
+```
+go tool pprof -http=:9090 cpu.prof
+```
+A flamegraph example would look like the following:
+
+<img src="flamegraph.png" height="50%">