Feature: extend genCA/genCAWithKey/genSignedCert/genSignedCertWithKey to support not only CN, but other fields as well

[aodinokov]

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getCA, genSignedCert and friends right now support only CN field.

For some applications it's necessary to provide other parameters that pkix.Name supports [1]. E.g. I've tried to use Sprig to generate k8s CA and admin cert, but in openssl it's necessary to provide: /CN=admin/O=system:masters, and it's not possible to generate k8s admin cert with sprig because of that. I've created the Extended version of that functions [2]. If the parameter doesn't have / it behaves like the current implementation, but if the first symbol is / it tries to parse it as RFC 2253 Distinguished Names syntax similar to what openssl does. Here is the implementation of the function that converts that [3]. Another option I was thinking about - instead of RFC 2253 format it's possible to unmarshal Name structure from some format (e.g. yaml etc) and use it as a parameter.

If the Sprig community needs RFC 2253 implementation, I could create a PR based on the work I have already done. Please let me know.

Cheers! [1]

			pkix.Name{
				CommonName:         `CN`,
				SerialNumber:       `SN`,
				Country:            []string{`C1`, `C2`},
				Organization:       []string{`O1`, `O2`},
				OrganizationalUnit: []string{`OU1`, `OU2`},
				Locality:           []string{`L1`, `L2`},
				Province:           []string{`ST1`, `ST2`},
				StreetAddress:      []string{`S1`, `S2`},
				PostalCode:         []string{`PC1`, `PC2`},

[2] https://github.com/airshipit/airshipctl/blob/master/pkg/document/plugin/templater/extlib/crypto.go

[3] https://github.com/airshipit/airshipctl/blob/master/pkg/document/plugin/templater/extlib/crypto.go#L145