fix: add #EOF sentinel chars to custom search file

[jackfrancis]

Reason for Change:

This PR adds the needed #EOF sentinel chars to the custom search domains script so that the CSE file wait func will properly detect its arrival on disk via cloud-init.

Issue Fixed:

Fixes #3859

Credit Where Due:

Does this change contain code from or inspired by another project?

• No
• Yes

If "Yes," did you notify that project's maintainers and provide attribution?

• No
• Yes

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[codecov]

Codecov Report

Merging #3862 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3862   +/-   ##
=======================================
  Coverage   72.83%   72.83%           
=======================================
  Files         149      149           
  Lines       23171    23171           
=======================================
  Hits        16876    16876           
  Misses       5178     5178           
  Partials     1117     1117           

Impacted Files	Coverage Δ
pkg/engine/templates_generated.go	48.65% <ø> (ø)

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[mboersma]

/lgtm

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis, mboersma

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