fips: allow more RSA modulus sizes

Previously, we restricted RSA modulus size to be either 2048 or 3072 bits in FIPS mode, following FIPS 186-4. On the other hand, FIPS 140-2 IG A.14 and FIPS 140-3 IG C.F updates it to allow arbitrary modulus sizes equal to or larger than 2048 bits under certain conditions.

This change reflects the guidance, though it only allows known sizes due to the complexity of calculating the approximate security strength using the formula in FIPS 140-2 IG 7.5.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• Code modified for feature
• Test suite updated with functionality tests
• Test suite updated with negative tests
• Documentation updated / NEWS entry present (for non-trivial changes)
• CI timeout is 2h or higher (see Settings/CICD/General pipelines/Timeout)

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code