Implement support for x509 extra extensions

[AbdulRahmanAlHamali]

This PR provides the ability to add arbitrary extensions to certificates and certificate requests, by providing their OID, whether they are critical or not, and their value.

The value of the extension is serialized into Abstract Syntax Notation One (ASN.1)

The PR only implements a few of the possible types for value, but makes it very easy to add more types upon demand.

Please let me know what you think, looking forward to the review.

Regards,

[hashicorp-cla]

Thank you for your submission! We require that all contributors sign our Contributor License Agreement ("CLA") before we can accept the contribution. Read and sign the agreement

Learn more about why HashiCorp requires a CLA and what the CLA includes

---

AbdulRahman AlHamali seems not to be a GitHub user. You need a GitHub account to be able to sign the CLA. If you already have a GitHub account, please add the email address used for this commit to your account.

_{Have you signed the CLA already but the status is still pending? Recheck it.}

[Karthikeyanraman94]

HI Team, can we have this merged, we literally need this feature for one of our client certificate

[Karthikeyanraman94]

@julienduchesne : Could you please help this feature go live... We actually require OID feature for few of our client certs.. And this will be more helpfull