refactor: Unifies DPoP and client signing keys

[dmihalcik-virtru]

• Currently, the js client generates two different RSA keypairs for signing the DPoP proofs and the 'signed request token' - the body of the rewrap request. This removes the duplication and instead uses the same keypair to sign both the DPoP proofs and the rewrap request. This is required by the new go KAS implementation, which uses the DPoP key when present to validate the rewrap body

[github-actions]

If these changes look good, signoff on them with:

git pull && git commit --amend --signoff && git push --force-with-lease origin

If they aren't any good, please remove them with:

git pull && git reset --hard HEAD~1 && git push --force-with-lease origin

[sonarqubecloud]

Quality Gate passed

Issues
4 New issues
0 Accepted issues

Measures
0 Security Hotspots
85.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud