TrustAnchor does not support PKCS#1

[f11h]

Describe the bug

When creating TrustAnchor signatures the CLI currently does not support private keys in PKCS#1 format.
Doing this results in:

org.bouncycastle.openssl.PEMException: problem parsing PRIVATE KEY: java.lang.IllegalArgumentException: unknown object in getInstance: org.bouncycastle.asn1.ASN1Integer
        at org.bouncycastle.openssl.PEMParser$PrivateKeyParser.parseObject(Unknown Source)
        at org.bouncycastle.openssl.PEMParser.readObject(Unknown Source)
        at eu.europa.ec.dgc.cli.utils.CliUtils.readKeyFromFile(CliUtils.java:50)
        at eu.europa.ec.dgc.cli.trustanchor.Sign.call(Sign.java:83)
        at eu.europa.ec.dgc.cli.trustanchor.Sign.call(Sign.java:47)
        at picocli.CommandLine.executeUserObject(CommandLine.java:1953)
        at picocli.CommandLine.access$1300(CommandLine.java:145)
        at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2352)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2346)
        at picocli.CommandLine$RunLast.handle(CommandLine.java:2311)
        at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2179)
        at picocli.CommandLine.execute(CommandLine.java:2078)
        at eu.europa.ec.dgc.cli.Main.main(Main.java:28)
Caused by: java.lang.IllegalArgumentException: unknown object in getInstance: org.bouncycastle.asn1.ASN1Integer
        at org.bouncycastle.asn1.ASN1Sequence.getInstance(Unknown Source)
        at org.bouncycastle.asn1.x509.AlgorithmIdentifier.getInstance(Unknown Source)
        at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.<init>(Unknown Source)
        at org.bouncycastle.asn1.pkcs.PrivateKeyInfo.getInstance(Unknown Source)
        ... 13 more

Expected behaviour

dgc ta sign -c cert_ta.pem -k key_ta-unenc.pem -i cert.pem

with a PKCS#1 PrivateKey should succesfully sign a certificate with TrustAnchor.

Steps to reproduce the issue

1. Create Cert --> openssl req -x509 -newkey rsa:4096 -keyout key.pem -out cert.pem -days 365
2. Create TA --> openssl req -x509 -newkey rsa:4096 -keyout ta-key.pem -out ta-cert.pem -days 365
3. Unencrypt Key --> openssl rsa -in ta-key.pem -out ta-unenc.pem
4. Try to sign -->dgc ta sign -c ta-cert.pem -k ta-unenc.pem -i cert.pem

Workaround

See #4 for a workaround

Possible Fix

The problem is in eu.europa.ec.dgc.cli.utils.CliUtils#readKeyFromFile method. This method only tries to parse content of pem file into PrivateKeyInfo. This should be reworked in order to support other Private Key format.