fix: #28762 - fix missing command in /help

[adarshlilha]

fix missing command for: "Mark all messages as read" - under /help
closes #28762

Proposed changes (including videos or screenshots)

When using /help command in any room the rocket.cat bot lists all keyboard shortcuts for the operations that can be done in rocket chat but for one command(marking all messages as read) shortcut is not being renderered

before fix screenshot:

post fix screenshot:

Issue(s)

closes #28762

Steps to test or reproduce

• open any channel
• type "/help" and press enter(return) key
• bot responds with a list of commands with their description
• notice here for 2nd command - "Mark all messages as read" - the shortcut command is missing

all commands must have the shortcut command as well

Further comments

this PR adds the missing placeholder for mark all messages as read command for English(en) language

[codecov]

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