feat: parse and re-use admin token username

[TJM]

This will parse the username from the current token and re use it for the new one during rotation.

It will default to "admin" if the subject parsing doesn't work.

[alexhung]

LGTM. This reminds me that we need to add more tests 😄

[TJM]

I did test this against our Artifactory 7.38 instance here. For all that is worth. Automated tests would be a "good thing" (tm)

[shrajfr12]

lgtm

[TJM]

This allows you to name your access token something reasonable like vault-artifactory-admin ... I am not sure which version of artifactory required the username to specifically be admin, but on a reasonably recent version, that is no longer the case, and can make debugging issues much easier.

[alexhung]

@TJM Don't quote me on this, but I think it's the switch to scoped token that remove the restriction of admin username. However, this doesn't mean you can use any username as it still needs to match with a valid username in Artifactory.

[Turhsus]

LGTM, nice catch