Set Java 8 as minimum required version (#874)

- Upgraded Bouncy Castle from 1.70 to 1.75
- Upgraded SLF4J from 1.7.36 to 2.0.7
- Upgraded Logback from 1.2.11 to 1.3.8
- Upgraded Apache MINA SSHD from 2.8.0 to 2.10.0
- Upgraded Grizzly HTTP Server from 2.4.4 to 3.0.1
- Upgraded Testcontainers from 1.16.2 to 1.18.3
- Refactored references and removed HttpClient dependency
- Upgraded GitHub Actions setup-java from 1 to 3
- Updated GitHub Actions to use Temurin JDK 11
- Added OpenSSL upgrade to RSA Key Tests

Co-authored-by: Jeroen van Erp <jeroen@hierynomus.com>

README.adoc

@@ -95,7 +95,11 @@ If you need something that is not included, it shouldn't be too hard to add (do
 http://ssh-comparison.quendi.de/comparison.html[SSH Implementation Comparison]
 
 == Dependencies
-Java 7+. http://www.slf4j.org/download.html[slf4j] is required. http://www.bouncycastle.org/java.html[bouncycastle] is highly recommended and required for using some of the crypto algorithms.
+
+- Java 8 or higher
+- https://www.slf4j.org/[SLF4J 2.0.0]
+- https://www.bouncycastle.org[Bouncy Castle]
+
 
 == Reporting bugs
 Issue tracker: https://github.com/hierynomus/sshj/issues