Replace juju/ratelimit with x/time/rate

[mjg59]

The consequences of the LGPL static linking exception in juju/ratelimit
aren't terribly well understood, and it's the only component in the
certificate-transparency chain that's not under something well-studied like
MIT or Apache. There's now ratelimit support in x/time, so porting over to
use that instead simplifies licensing analysis.

Checklist

• I have updated the CHANGELOG.
  • Adjust the draft version number according to semantic versioning rules.
• I have updated documentation accordingly.

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[google-cla]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

📝 Please visit https://cla.developers.google.com/ to sign.

Once you've signed (or fixed any issues), please reply here with @googlebot I signed it! and we'll verify it.

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What to do if you already signed the CLA

Individual signers

• It's possible we don't have your GitHub username or you're using a different email address on your commit. Check your existing CLA data and verify that your email is set on your git commits.

Corporate signers

• Your company has a Point of Contact who decides which employees are authorized to participate. Ask your POC to be added to the group of authorized contributors. If you don't know who your Point of Contact is, direct the Google project maintainer to go/cla#troubleshoot (Public version).
• The email used to register you as an authorized contributor must be the email used for the Git commit. Check your existing CLA data and verify that your email is set on your git commits.
• The email used to register you as an authorized contributor must also be attached to your GitHub account.

ℹ️ Googlers: Go here for more info.

[pphaneuf]

"Your first contribution to a Google open source project"... 🤣

/gcbrun

[pphaneuf]

Looks like you, er, need to sign the CLA?

[mjg59]

Yup, just blocked on legal for a moment.

[pav-kv]

Let's resurrect this PR.

[pav-kv]

/gcbrun

[pav-kv]

/gcbrun

[pav-kv]

@mjg59 The check still stays you haven't signed the CLA. Please do if you would still like this PR submitted. I rebased it on top of the current master so that it has no conflicts.

[mjg59]

CLA should now be signed

[mjg59]

Oh I see my corp email address isn't on file. I'll deal with that in the morning, sorry!

[mjg59]

@googlebot I signed it!

[pav-kv]

@mjg59 Looks like the bot finally believed you, thanks :)