Allow mappings in the filename when exporting issues

Description

Allow mappings to be used in the filename when exporting single or multiple issues in Xporter Cloud.

Currently, mappings can be used in filenames for Scheduled Reports and Workflow Post Functions, but this option is not available when exporting issues manually.

User friction
Users cannot customize the filename using mappings when manually exporting issues. If they need the filename to contain information from the issue, they must rename the exported file manually.

Steps to reproduce (right now)

1. Open an issue or select multiple issues.
2. Export the issue(s) using Xporter.
3. Select the template and output format.
4. Modify Output file name

Actual Result:

Mappings cannot be used in the filename when manually exporting single or multiple issues.

IMPACT

What would improve if solved:
Users would be able to use mappings such as Issue Key, Summary, or other fields in the filename when exporting issues.

For example:

Report_${Key}.pdf

Impact on stakeholders:
This would reduce manual work for users who regularly export documents and make exported files easier to identify and organize.

Current workaround:
Users can use Scheduled Reports or Workflow Post Functions, where mappings in filenames are supported, or manually rename the files after exporting.

CONTEXT & EXAMPLES:

Concrete example:

A user wants to export an issue and include its Issue Key in the filename:

Report_${Key}.pdf

For issue TEST-123, the expected filename would be:

Report_TEST-123.pdf

Currently, this cannot be configured during a manual export.

Workaround risk:

Manually renaming exported files adds extra work and may lead to inconsistent or incorrectly named files. Scheduled Reports and Workflow Post Functions may not be suitable when users need to manually export issues.