Updating and simplifying templates

[x9136]

Description

I suggest some changes to the templates to remove unnecessary information and clarify what is needed from the contributor.

Type of change

❌ Bug fix (non-breaking change which fixes an issue)
✅ General change (non-breaking change that doesn't fit the above categories, such as copyediting)

Changelog

• Removed [DISCUSSION] from the issue template because it was duplicating the label.
• Shortened the subheadings in the icon addition template because they were duplicating the header.
• Removed the note about the icon being added from the request form, because that wasn't used and you can see in the current requests table what requests are fulfilled.
• Removed the indentation in the icon lists to make it easier to read.
• Renamed the package name example to make it closer to the real ones.
• Simplified the entry to add links because the @drawable/package part was unclear.
• Clarified in the PR template what actions to take. In particular it was not obvious that the template could be inserted into the description if you clicked on the link.

[x9136]

The preview doesn't take line breaks into account, but I think it should be fine since the General change template works as espected once selected.