feat: add support for PostgreSQL application_name in DSN

[myalcin81]

Description PostgreSQL has application_name support and its implemented.

Checklist:

• [ ] Securely signed commits
• [ ] Component(s) with PHPDoc blocks, only if necessary or adds value
• [ ] Unit testing, with >80% coverage
• [ ] User guide updated
• [ ] Conforms to style guide

[kenjis]

You can configure it as:

    public array $default = [
        'DSN'=> "host=localhost port=5432 user=postgres password='postgres' dbname=test options='--application_name=CI4'",
        // ...
    ]; 

So this is an enhancement. So you should send this PR to 4.6 branch. See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/workflow.md#if-you-sent-to-the-wrong-branch

[kenjis]

Thank you for sending this PR!

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[kenjis]

[!IMPORTANT] We expect all code changes or bug-fixes to be accompanied by one or more tests added to our test suite to prove the code works.

This PR does not have the necessary test code. If you want this PR to be reviewed, please add the test code. See https://github.com/codeigniter4/CodeIgniter4/blob/develop/contributing/pull_request.md#unit-testing

If the test is not added, this PR will be closed.