Add support for opening external programs in infoclick

[linusfj]

Description
The current infoclick functionality does not support including links that open external programs, causing inconvenience for users. They must manually switch between programs or use less efficient workarounds while working with infoclick.

Example
In the layers configuration file, the link can look like the example below:
a href=\"appcontainer:ExternalApp/OpenIssue?issueid={issueid}

However, when rendered in infoclick, it is converted to a href="javascript:void(0)", which results in a client error and prevents the link from functioning as intended.

Suggested solution
Implement a feature that allows users to include links within infoclick that can open external programs, such as installed desktop applications or other non-browser-based tools.

[Hallbergs]

I've had a look at this.

When we're using markdown, the component rendering the markdown does some uri-transformations. (We're using react-markdown, see: their GitHub page.

React-markdown makes sure that the provided url follows a few rules, one of which is that the protocol has to be one of the following: const protocols = ['http', 'https', 'mailto', 'tel']. I found no way to allow for protocol injection to the component...

However, i found that the uri-tranformer can be overridden, see below:

        <ReactMarkdown
          transformLinkUri={(x) => x}
          remarkPlugins={[gfm]} // GitHub Formatted Markdown adds support for Tables in MD
          rehypePlugins={rehypePlugins} // Needed to parse HTML, activated in admin
          components={this.components} // Custom renderers for components, see definition in this.components
          children={this.markdown} // Our MD, as a text string
        />

We could create out own function and pass it in the transformLinkUri-prop. If we would do that, we could allow for setting allowed protocols in appConfig.json for example.

I made a quick test with transformLinkUri={(x) => x} and it worked as expected, see below:

[Hallbergs]

Added a solution that could possibly work. Feel free to check out and test for yourself.

[jacobwod]

I'll check it out later today, seems promising!

[Hallbergs]

I added the setting to admin as well in the branch

[lina-sbk-gbg]

I have tested now and it works very well. However, the check box in admin does not seem to read the saved value in the config file. The checkbox is checked regardless of the value in config. Could it be related to the .NET backend or is it the same in NodeJS?

Great job regardless!

[jacobwod]

PR please, @Hallbergs?