RFR: 8103: Add user configuration for local JVM refresh interval

[Alex Macdonald]

This PR addresses JMC-8103 [[0]](https://bugs.openjdk.org/browse/JMC-8103), in which it would be nice to have a user control for adjusting the rate at which the JVM browser discovers JVMs.

At the moment, the `LocalDescriptorProvider` scans every 5s for differences in local JVMs, and then goes through the process of creating a local descriptor, attaching, populating the jvm browser, etc.

This PR adds an extra field to the Preferences under `Preferences -> JVM Browser -> Local` that lets the user specify how frequently (or infrequently) this scan should occur. As mentioned at the latest upstream community meeting, this value should probably have a lower-bound as to not scan too often, so I've selected 1000 ms to match similar refresh rates of the jvm browser.

![example](https://github.com/openjdk/jmc/assets/10425301/4dbe363f-a3d4-4513-9654-f99cfe71aaeb)


[0] https://bugs.openjdk.org/browse/JMC-8103

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Commit messages:
 - 8103: Add user configuration for local JVM refresh interval

Changes: https://git.openjdk.org/jmc/pull/508/files
 Webrev: https://webrevs.openjdk.org/?repo=jmc&pr=508&range=00
  Issue: https://bugs.openjdk.org/browse/JMC-8103
  Stats: 45 lines in 6 files changed: 37 ins; 1 del; 7 mod
  Patch: https://git.openjdk.org/jmc/pull/508.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/508/head:pull/508

PR: https://git.openjdk.org/jmc/pull/508