Remove duplicate point and fix date format

[Victor-Nyagudi]

Summary

Removed a duplicate bullet point on the "Why and how to contribute" page.

I kept the second bullet point because it's the most recent one added in this commit.

I kept the first bullet point because the docs recommend, as a best practice, to use newtabref for links navigating away from developers.mattermost.com.

The date in e2e-cheatsheets.md used a format that wasn't parsable leading to this error when I ran make run.

ERROR the "date" front matter field is not a parsable date: 
see /{Path from my Mac}/mattermost-developer-documentation/site/content/contribute/more-info/webapp/e2e-cheatsheets.md

It seems the author forgot to add the seconds in the time format leading to an error. I can see from the current date they meant the time to be exactly midnight, so I added some zeroes for the seconds.

The date now uses one of the parsable formats recommended by the Hugo documentation.

Ticket Link

N/A

[mattermost-build]

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[Victor-Nyagudi]

cc: @cwarnermm

Discussed the change first in the Mattermost Content channel.

[github-actions]

Newest code from Victor-Nyagudi has been published to preview environment for Git SHA 56a0e79

[Victor-Nyagudi]

Thought I'd fix that sentence in this PR as well.

Discussed it first in this channel.

Didn't know master had already been merged into this PR so I didn't pull the changes first resulting in divergent branches.

I used git config pull rebase false before pulling the changes hence the duplicate commits. Hope that doesn't complicate things too much.

Is a "squash and merge" a viable option here?

[cwarnermm]

Thank you, @Victor-Nyagudi!