proposal: Add placeholders

[Andre601]

Is your feature request related to a problem? Please describe.
From what I can tell (And what I tested so far) can you not just use something like ${{ github.event.sender.login }} to display the name of the person opening the issue/Pull request.

Describe the solution you'd like
It would be nice to have some placeholders which could be used for things like the name of the person opening the issue/Pull request.

This would allow messages like Thank you @{user} for reporting this bug! which would be translated to Thank you @Andre601 for reporting this bug! and mention the user in the process.

Describe alternatives you've considered
There doesn't seem to be any alternatives available

Additional context

[peaceiris]

I have released v1.4.0-0 and tested at #158.

actions-label-commenter/.github/label-commenter-config.yml

Lines 39 to 44 in 82e5fad

	- name: proposal
	labeled:
	issue:
	body: |
	Thank you @{{ sender.login }} for suggesting this.
	The maintainer will reply.

Could you test v1.4.0-0? And, do you have any ideas about another useful variable?

[Andre601]

It does work.

And I at most can think of perhaps a placeholder to list asigned people for the PR/issue.
Maybe something like {{ assignees }} for a comma separated list of assigned people and {{ assignees.n.login }} for a specific one (n would be a 0 indexed number) and if nothing is there, the placeholder wouldn't be changed.
And maybe in case someone wants this {{ assignees.mention }} which would return the names of each assignee as a mention.

[Andre601]

I find an issue using {{ sender.login }}

It seems to use whoever last replied to, or performed actions on an issue/PR even if the creator of it is a different one.
For example if ExampleUser creates an issue and I assign a label that responds with Hello @{{ sender.login }} will the result be Hello @Andre601

[peaceiris]

@{{ issue.user.login }} is available now.

issue: #261
pr: #272