http: improve AWS HTTP v4 Signature auth

- Add support services without region and service prefixes in
the URL endpoint (ex. Min.IO, GCP, Yandex Cloud, Mail.Ru Cloud Solutions, etc)
by providing region and service parameters via aws-sigv4 option.
- Add [:region[:service]] suffix to aws-sigv4 option;
- Fix memory allocation errors.
- Refactor memory management.
- Use Curl_http_method instead() STRING_CUSTOMREQUEST.
- Refactor canonical headers generating.
- Remove repeated sha256_to_hex() usage.
- Add some docs fixes.
- Add some codestyle fixes.
- Add overloaded strndup() for debug - curl_dbg_strndup().
- Update tests.

Closes #6524

tests/data/test1933

@@ -40,14 +40,14 @@ crypto
 </features>
 
 <name>
-HTTP AWS_SIGV4
+HTTP AWS_SIGV4 with one provider and auth cred via URL
 </name>
 <tool>
 lib1933
 </tool>
 
 <command>
-http://%HOSTIP:%HTTPPORT/1933/testapi/test
+http://xxx:yyy@%HOSTIP:%HTTPPORT/1933/testapi/test
 </command>
 </client>
 
@@ -61,8 +61,8 @@ http://%HOSTIP:%HTTPPORT/1933/testapi/test
 <protocol>
 GET /1933/testapi/test HTTP/1.1
 Host: %HOSTIP:%HTTPPORT
-X-yyy-Date: 19700101T000000Z
-Authorization: XXX4-HMAC-SHA256 Credential=xxx/19700101/0/127/xxx4_request, SignedHeaders=content-type;host;x-yyy-date, Signature=b125a904e7f5cc1f553d8f3682947eb003c4ca6c504097c0dc2d9323289bfcdd
+Authorization: XXX4-HMAC-SHA256 Credential=xxx/19700101/0/127/xxx4_request, SignedHeaders=content-type;host;x-xxx-date, Signature=d2c2dff48c59ec49dc31ef94f18c5dc1ac3eae2a70d51633a4342dadc0683664
+X-Xxx-Date: 19700101T000000Z
 
 </protocol>
 </verify>