Using `[` in ticket names created with Camptix causes an error with the Stripe API.

Describe the bug

When using Stripe payment for ticket purchases in Camptix, if the ticket name contains [, an error occurs in the Stripe API response. This is because the Stripe API specification interprets the string inside [] as an object key. To resolve this issue, the clean_metadata function needs to replace [] with another character like ().

To reproduce

Create a new ticket and include the [ string, e.g., 6/2 – Micro Sponsor [ 10USD ]
Enable Camptix Stripe Payment (it's okay to use sandbox mode)
Try to order this ticket from the Ticket page
You will encounter an error when creating a new Stripe Checkout Session
Expected behavior

The ticket name needs to be included in the metadata of the Stripe Payment Intent object when creating Stripe Checkout Sessions API. e.g.: $args['payment_intent_data']['metadata']['6/2 [Sponsor ticket]'] = '1';

**Expected Behavior The ticket name needs to be included in the metadata of the Stripe Payment Intent object when creating Stripe Checkout Sessions API. e.g.: $args['payment_intent_data']['metadata']['6/2 [Sponsor ticket]'] = '1';

Actual Behavior**

Due to the Stripe API specification, a text inside the [] will be converted to an object key like the following:

$args['payment_intent_data']['metadata']['6/2 [Sponsor ticket]'] = '1';
->
{
  "metadata": {
    "6/2": {
      "Sponsor ticket": "1"
    }
  }
}

Suggestion In the clean_metadata function, we may need to replace the [] string with another character like () instead.

$key = $this->trim_string( $key, 40, '' );
$key = str_replace( '[', '(', str_replace( ']', ')', $key ) );

When we avoid passing the [] string as the key of the metadata, the Stripe API request will work correctly.

This idea seems reasonable, and if you approve, I'll proceed with creating a new pull request for this.

Screenshots

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WordCamp

If this is a problem on a specific WordCamp's site, list the site or page URL here.

At the WordCamp Kansai 2024, we suffered from this error: https://kansai.wordcamp.org/2024/wp-admin/post.php?post=3772&action=edit

System (please complete the following information):

Device: [e.g. laptop, iPhone6]
OS: [e.g. iOS]
Browser [e.g. chrome, safari]
Version [e.g. 22]

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WordPress / wordcamp.org

Using `[` in ticket names created with Camptix causes an error with the Stripe API. #1270

Actual Behavior**