[windows installer script] Mark Fluentd support as deprecated

[crobert-1]

Description:
Follow up to #6264, for the Windows installer script this time.

Testing:

> Get-Help .\packaging\installer\install.ps1 -detailed
...
    -with_fluentd <Boolean>
        DEPRECATED: Fluentd support has been deprecated and will be removed in a future release.
        Please refer to documentation for more information: https://github.com/signalfx/splunk-ot
        el-collector/blob/main/docs/deprecations/fluentd-support.md
        (OPTIONAL) Whether to install and configure fluentd to forward log events to the
        collector (default: $false)
> .\packaging\installer\install.ps1 -with_fluentd $True
...
WARNING: [DEPRECATED] Fluentd support has been deprecated and will be removed in a future release.
 Please refer to documentation for more information:
https://github.com/signalfx/splunk-otel-collector/blob/main/docs/deprecations/fluentd-support.md

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.94%. Comparing base (95a48d6) to head (34d6dc8).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6362   +/-   ##
=======================================
  Coverage   44.94%   44.94%           
=======================================
  Files         390      390           
  Lines       27010    27010           
=======================================
  Hits        12139    12139           
  Misses      14004    14004           
  Partials      867      867           

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