RFR: 8296125: Add a command line option to set a refresh rate of the OS cached metrics in Linux

[Olga Mikhaltsova]

I would like to add a new command line product option:
-XX:OsCachedMetricsRefreshRate=value, -
where a value is times per second and is in the range [1; 1000000000].

It substitutes the hardcoded timeout of 20 ms between re-readings of the OS cached metrics introduced in [JDK-8232207](https://bugs.openjdk.org/browse/JDK-8232207) and allows to set this timeout (as a refresh rate) by a user at the launch time.

This option will be available only on Linux.

It can be used as followed:
java -XX:OsCachedMetricsRefreshRate=100 MyApp

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Commit messages:
 - 8296125: Add a command line option to set a refresh rate of the OS cached metrics in Linux

Changes: https://git.openjdk.org/jdk/pull/10918/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10918&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8296125
  Stats: 18 lines in 5 files changed: 12 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10918.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10918/head:pull/10918

PR: https://git.openjdk.org/jdk/pull/10918