Mattermost-plugin-github: Remove commented text in Tooltip link body

[mickmister]

Currently the link tooltip includes the contributing instructions in the body of the issue/PR. It is a bit noisy and doesn't convey the important information in the PR's description.

[hanzei]

Let's go this server-side

[abdulsmapara]

I would like to give this a try.

[abdulsmapara]

I am thinking to use regular expressions for removing commented text inside <!-- -->.

[hanzei]

Thanks for taking a look @abdulsmapara.

Regular expressions are definitiv a valid approach to solve this issue.

[mickmister]

@abdulsmapara There was a PR that did this sort of fix for notifications. Could the same regex be used here?
https://github.com/mattermost/mattermost-plugin-github/pull/172
https://github.com/M-ZubairAhmed/mattermost-plugin-github/blob/ddab50ecf135f43ce6018fcab004aa9658f5ffbb/server/template.go#L13

[abdulsmapara]

@mickmister, I have exactly considered the same regex present in template.go to avoid redundancy.