Update opensaml dependency to 4.1.0

[jkakavas]

opensaml 4.1.0 was released on 23/04/21. We should look into upgrading our dependencies for the SAML realm and the Identity Provider implementations

• Investigate major API changes between 3.4.5 and 4.1.0
• Look into release notes for bugs resolved and major functionality additions

[elasticmachine]

Pinging @elastic/es-security (Team:Security)

[tvernum]

OpenSAML 4.0 requires Java 11.
We cannot upgrade in the 7.x development tree.

[tvernum]

I've started work on this in #77012

There's a few issues to work out, but most of them seem to be solvable except OpenSAML4 seems to have a hard dependency on the standard (non-FIPS) distribution of BouncyCastle.
It requires org.bouncycastle.jce.ECNamedCurveTable which doesn't exist in BCFIPS.
This makes it very difficult for us, because we want to support SAML when running in FIPS mode, and we can't do that (at least, not easily) if the BC jars are also on the classpath.

[tvernum]

We've upgraded to v4.0 in #77012, but could not upgrade to v4.1 due to an incompatibility with FIPS.
I'm leaving this issue open so that we can look at it again in the future.