Improve VTOrc config handling to support dynamic variables

[GuptaManan100]

Description

This PR changes how config files are handled in VTOrc, moving them to use viper instead of the custom solution previously employed. This change allows the following parameters to be dynamically loaded -

1. InstancePollTime
2. PreventCrossCellFailover
3. SnapshotTopologyInterval
4. ReasonableReplicationLag
5. AuditToBackend
6. AuditToSyslog
7. AuditPurgeDuration
8. WaitReplicasTimeout
9. TolerableReplicationLag
10. TopoInformationRefreshDuration
11. RecoveryPollDuration

Related Issue(s)

• Fixes Feature Request: Handle config in VTOrc using Viper #17217

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

Review Checklist

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• Protobuf changes should be wire-compatible.
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• vtctl command output order should be stable and awk-able.

[codecov]

Codecov Report

Attention: Patch coverage is 41.96429% with 65 lines in your changes missing coverage. Please review.

Project coverage is 67.41%. Comparing base (0403d54) to head (897ab10).
Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/vtorc/config/config.go	42.25%	41 Missing ⚠️
go/vt/vtorc/server/api.go	9.09%	10 Missing ⚠️
go/vt/vtorc/logic/vtorc.go	0.00%	6 Missing ⚠️
go/viperutil/debug/debug.go	0.00%	4 Missing ⚠️
go/cmd/vtorc/cli/cli.go	0.00%	1 Missing ⚠️
go/vt/vtorc/discovery/queue.go	0.00%	1 Missing ⚠️
go/vt/vtorc/inst/instance_dao.go	87.50%	1 Missing ⚠️
go/vt/vtorc/logic/tablet_discovery.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17218      +/-   ##
==========================================
+ Coverage   67.34%   67.41%   +0.07%     
==========================================
  Files        1570     1570              
  Lines      252734   252867     +133     
==========================================
+ Hits       170204   170471     +267     
+ Misses      82530    82396     -134     

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[GuptaManan100]

This makrs the field dynamic