Fix SSL metrics for dynamically registered bundles

[Colorfulnia]

When SslMeterBinder is constructed, it only registers update handlers for the bundles
returned by sslBundles.getBundleNames() at that time. Bundles that are registered later
only trigger the register handler once and never get an update handler, so subsequent
SslBundleRegistry.updateBundle(...) calls do not refresh the ssl.chain.expiry gauges.

This change updates the register handler to also register an update handler for the
newly registered bundle and adds a regression test:

• SslMeterBinderTests.shouldWatchUpdatesForBundlesRegisteredAfterConstruction

The test fails with the original implementation and passes with this change.

Fixes #48144 (gh-48144)

[wilkinsona]

Thanks for the PR, @Colorfulnia. It contains a commit authored by @TerryTaoYY. Judging by the user profiles, I think this may be two different accounts owned by the same person but, AFAIK, we can't accept a PR from one user that contains commits from another user.

[Colorfulnia]

@wilkinsona Thank you for let me know, I will re-pull request with a single account.

[TerryTaoYY]

Thanks for the PR, @Colorfulnia. It contains a commit authored by @TerryTaoYY. Judging by the user profiles, I think this may be two different accounts owned by the same person but, AFAIK, we can't accept a PR from one user that contains commits from another user.

Thanks for the clarification. I've submitted a new pull request from a single account: #48153.