[Internal][BugFix] Call StarOsAgent.prepare once immediately following initialization instead of many times in other StarOsAgent methods and sometimes failing to do so

[ctbrennan]

Internal version of upstream PR StarRocks#54047

Why I'm doing:

I found some edge cases where StarOsAgent.serviceId was still empty in the non-leader FE and caused errors when users ran SHOW STORAGE VOLUMES or SHOW CREATE TABLE. It turned out that listFileStore and getFileStore happen to be missing calls to prepare which other functions have. I think we need to call prepare exactly once.

What I'm doing:

The simplest way to fix this would be to call prepare in all StarOsAgent methods which use serviceId but I think this is the wrong approach. Instead I'm doing the following:

1. Removing the call to StarOsAgent.init from GlobalStateMgr.intitialize. This call is doing nothing since we're calling starOsAgent with a null server and it's overwritten when StarRocksFE.start calls StarMgrServer.initialize soon afterwards.
   1. This simplifies things by ensuring that we're only calling starOsAgent.init in one place.
2. Having StarMgrServer call StarOsAgent.prepare as soon as it's possible to do so, therefore ensuring that serviceId is populated before the agent is used.
3. Removing all redundant prepare calls from other StarOsAgent methods.

Fixes #issue

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
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Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

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