minorfix: set default fluid file prefetcher sidecar image

[TrafalgarZZZ]

Ⅰ. Describe what this PR does

Add the following values in values.yaml to allow users to configure Fluid's file prefetcher sidecar container's image:

filePrefetcher:
  imagePrefix: *defaultImagePrefix
  imageName: fluid-file-prefetcher
  imageTag: v0.1.0

File prefetcher's Dockerfile can be found at tools/file-prefetcher/Dockerfile

Ⅱ. Does this pull request fix one issue?

NONE

Ⅲ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[sonarqubecloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cheyang]

/lgtm
/approve

[fluid-e2e-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cheyang

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