crypto/acme: Add support for custom validity certs

[daknob]

This commit allows autocert to request certificates with a specific notAfter value from the ACME CA. The CA may choose to honor this request or not. The acme package already supports this functionality, this CL brings this support to autocert as well.

[gopherbot]

This PR (HEAD: 4330f4eb88648b56a90e067f0f9c111b3f338bec) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/crypto/+/454175 to see it.

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[gopherbot]

Message from Antonios Chariton:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/454175. After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Antonios Chariton:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/454175. After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Maxime Tremblay:

Patch Set 2: Code-Review+1

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Please don’t reply on this GitHub thread. Visit golang.org/cl/454175. After addressing review feedback, remember to publish your drafts!