refactor: improve dependency injection capabilities

[aeneasr]

This PR addresses improvements to the OAuth2 package, making it easier to inject custom strategies. As part of this change, the HMAC strategy has been split into a prefixed and unprefixed strategy. Due to this, the instantiation of HMACSHAStrategy has changed.

This patch addresses improvements over #813 which has been reverted and fixed here.

BREAKING CHANGES: Going forward, please instantiate the HMACSHAStrategy using oauth2.NewHMACSHAStrategy():

-var hmacshaStrategy = oauth2.HMACSHAStrategy{
-	Enigma: &hmac.HMACStrategy{Config: &fosite.Config{GlobalSecret: []byte("foobarfoobarfoobarfoobarfoobarfoobarfoobarfoobar")}},
-	Config: &fosite.Config{
-		AccessTokenLifespan:   time.Hour * 24,
-		AuthorizeCodeLifespan: time.Hour * 24,
-	},
-}

+var hmacshaStrategy = oauth2.NewHMACSHAStrategy(
+	&hmac.HMACStrategy{Config: &fosite.Config{GlobalSecret: []byte("foobarfoobarfoobarfoobarfoobarfoobarfoobarfoobar")}},
+	&fosite.Config{
+		AccessTokenLifespan:   time.Hour * 24,
+		AuthorizeCodeLifespan: time.Hour * 24,
+	},
+)

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

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