Add API for manipulating Git hooks

[segevfiner]

This adds API support for manipulating Git hooks. Accompanying PR for a PR against Gitea: go-gitea/gitea#6436

[segevfiner]

@zeripath I based this on the existing API for web hooks, which doesn't seem to escape. Actually, I'm not seeing any reference to PathEscape in the entire SDK. So if I add escaping here, that will be the only place in the SDK that this would be done. So are you sure you want me to do this in this PR?

I couldn't find a function named PathSegmentsEscape, but should we add escaping here, we only need the normal PathEscape anyhow, as it's just the name of the hook which is a simple string without slashes.

P.S. If you are already looking at escaping URL components. An alternative way to build URLs with correct escaping is to use a library/package that implements RFC 6570 - URI Template level 4 to build the URLs which already handles escaping and should interface quite nicely with a project that uses Swagger (Swagger/OpenAPI v3 was actually designed with it in mind).

[zeripath]

We have to start somewhere. But I guess we'll have to do a refactor to actually escape all this stuff properly.

In terms of using templates to build URIs I suspect that any code that uses this will be bulky and verbose. Go doesn't have named function arguments, so you're then suggesting passing in either structs or maps to get the named arguments. Of course you can just use the go html template but even then you're probably going to end up with bulky code and you still have to pass in named arguments as a map or use numeric arguments.

Now there is an alternative and that is to get swagger or something else to generate this for us - this would clearly be the best idea but again that's a massive refactor. (I'm perfectly happy with bulky code so long as I never need look at it.)

Ok if you don't want to do the escaping I will approve but it really does need fixing - it doesn't exactly engender confidence in our code to see obvious escaping errors.