allure-robotframework not supporting link issue pattern

#### I'm submitting a ...
- [ ] bug report
- [x ] feature request
- [ ] support request => Please do not submit support request here, see note at the top of this template.

#### What is the current behavior?
When creating allure results with allure-robotframework it doesn't support parameterized way for creating prefix for issue links. For example if robot test contains TAG "issue:myIssueId", allure results (and generated allure report) will contain URL into host where allure report is served (like http://10.251.83.101:65165/myIssueId).

Current workaround is to place URL into test TAG, e.g. issue:https://myJira.com/browse/myIssueId, This shows whole URL in the linkname on allure report.

#### What is the expected behavior?
Possibility to have parameterized base URL to issue tracking system that is copied in the front of issueId instead host where report is served. For example command line switch or property file that includes key-value pair like "allure.link.issue.pattern=https;//myJira.com/browse/". Then allure robotframework listener should add this value in front of issue link URL.

#### What is the motivation / use case for changing the behavior?
Generated allure report link section is more readable, when link name is shorter and URL is not shown on the report.

#### Please tell us about your environment:

- Allure version: 2.1.0
- Test framework: allure-python 2.9.43
- Allure adaptor: allure-robotframework 2.9.43

从处理 Robot TAG values 的 allure-robotframework listener 开始，检查 issue links 的构建方式。检查现有的命令行或属性文件配置入口；当可配置的 issue-link base URL 为 issue ID 添加前缀，同时报告显示较短的链接名称时，即视为完成。

由索引模型根据 Issue 内容生成。