feat: document ttl for api keys

[hperl]

Related Issue or Design Document

https://github.com/ory-corp/cloud/pull/7011

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
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• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

Further comments

[vinckr]

small change, otherwise top :)

[piotrmsc]

Not related directly to this change but I found a quirk while searching for the updated document in the deployment preview.

You click on Concepts -> APIs (https://docs-cty6n6vwk-ory.vercel.app/docs/api/)
There is a TIP bar that points you to read more about authorization with API Keys (https://docs-cty6n6vwk-ory.vercel.app/docs/concepts/personal-access-token)
You open it and you end in the navigation at Reference -> Operations -> API Keys

Now you go back to docs main page and reference section is different from the one you were previously. We have two reference sections : one in the left hand sidebar and
second on the top nav bar. Now items in left hand does not correlate 1:1 to with items in Reference on the top nav bar. This is quiet confusing.

@vinckr was it something recently added with structure redising?

all done :)

[vinckr]

lgtm