What does this PR aim to accomplish?:

Extend the meaning of “PRIVATE KEY” in the webserver.tls.cert description to include RSA and ECC keys.

How does this PR accomplish the above?:

The term “RSA PRIVATE KEY” has been replaced with the more general “PRIVATE KEY,” as ECC keys are also accepted.

Link documentation PRs if any are needed to support this PR:

Please note that keys based on “Curve25519” and “Curve 448” (Ed25519/Ed448) for SSL/TLS server certificates are not yet supported by browsers, so they would cause an error during navigation if used.

According to the Baseline Requirements for TLS Server Certificates, specifically section 6.1.5, currently only RSA keys greater than 2048 bits and ECDSA keys (NIST P-256, NIST P-384, or NIST P-521) are accepted.

This is merely a note for future reference.

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