Update process.d/conf.yaml: fix the description of exact_match

[taromn]

What does this PR do?

This PR fixes the incorrect description of exact_match in process.d/conf.yaml

Motivation

The current explanation for exact_match is, "If you want to match your `search_string` on a substring within the list of process names, set this to true."

    ## @param exact_match - boolean - optional - default: true
    ## If you want to match your `search_string` on a substring within the list of process names, 
    ## set this to true. This is equivalent to running `ps -e` on Linux or `Get-Process` on Windows.

It means search_string: abc would match process names such as "abc_process", "abc.exe", ...

but actual implementation is, when exact_match is True, search_string should exactly match the process name, not just a substring.

https://github.com/DataDog/integrations-core/blob/024592040086a7901ed3614a93c0a9355b313d6f/process/datadog_checks/process/process.py#L162C1-L168C49

                        if exact_match:
                            if os.name == 'nt':
                                if proc.name().lower() == string.lower():
                                    found = True
                            else:
                                if proc.name() == string:
                                    found = True

Additional Note:
When exact_match is false, regular expression matching is used, so the current description might seem accurate in that case.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged