refactor: use struct types for claim related types (#283)

* oidc: add regression tests for token claim json

this helps to verify that the same JSON is produced,
after these types are refactored.

* refactor: use struct types for claim related types

BREAKING CHANGE:
The following types are changed from interface to struct type:

- AccessTokenClaims
- IDTokenClaims
- IntrospectionResponse
- UserInfo and related types.

The following methods of OPStorage now take a pointer to a struct type,
instead of an interface:

- SetUserinfoFromScopes
- SetUserinfoFromToken
- SetIntrospectionFromToken

The following functions are now generic, so that type-safe extension
of Claims is now possible:

- op.VerifyIDTokenHint
- op.VerifyAccessToken
- rp.VerifyTokens
- rp.VerifyIDToken

- Changed UserInfoAddress to pointer in UserInfo and
IntrospectionResponse.
This was needed to make omitempty work correctly.
- Copy or merge maps in IntrospectionResponse and SetUserInfo

* op: add example for VerifyAccessToken

* fix: rp: wrong assignment in WithIssuedAtMaxAge

WithIssuedAtMaxAge assigned its value to v.maxAge, which was wrong.
This change fixes that by assiging the duration to v.maxAgeIAT.

* rp: add VerifyTokens example

* oidc: add standard references to:

- IDTokenClaims
- IntrospectionResponse
- UserInfo

* only count coverage for `./pkg/...`

pkg/oidc/regression_data/oidc.IntrospectionResponse.json

@@ -0,0 +1,44 @@
+{
+	"active": true,
+	"address": {
+		"country": "Moon",
+		"formatted": "Sesame street 666\n666-666, Smallvile\nMoon",
+		"locality": "Smallvile",
+		"postal_code": "666-666",
+		"region": "Outer space",
+		"street_address": "Sesame street 666"
+	},
+	"aud": [
+		"foo",
+		"bar"
+	],
+	"birthdate": "1st of April",
+	"client_id": "777",
+	"email": "tim@zitadel.com",
+	"email_verified": true,
+	"exp": 12345,
+	"family_name": "Möhlmann",
+	"foo": "bar",
+	"gender": "male",
+	"given_name": "Tim",
+	"iat": 12000,
+	"iss": "zitadel",
+	"jti": "900",
+	"locale": "nl",
+	"middle_name": "Danger",
+	"name": "Tim Möhlmann",
+	"nbf": 12000,
+	"nickname": "muhlemmer",
+	"phone_number": "+1234567890",
+	"phone_number_verified": true,
+	"picture": "https://avatars.githubusercontent.com/u/5411563?v=4",
+	"preferred_username": "muhlemmer",
+	"profile": "https://github.com/muhlemmer",
+	"scope": "email phone",
+	"sub": "hello@me.com",
+	"token_type": "idtoken",
+	"updated_at": 1,
+	"username": "muhlemmer",
+	"website": "https://zitadel.com",
+	"zoneinfo": "Europe/Amsterdam"
+}