Create mechanism to send user survey DM

[superuser-does]

Description

We will collate a list of usernames for the survey we are looking to put out.

Our software allows us to generate a unique URL token for every invitation we put out. By doing this, we:

1. Will be able to segment the population of users in our analysis
2. Won't need a captcha!

We want to send a direct message to users we sample with a unique URL for each - and for that direct message to be localised.

Acceptance criteria

Given a table (or key-value pair) of usernames + unique URLs:

1. The /@/Lichess account must send a single direct message to all usernames
2. The direct message must accept a URL value from the table, which matches the recipient's username
3. The message must be sent in the user's language of choice, defaulting back to English if no translation is available

[superuser-does]

Need a developer opinion regarding the localised message:

We will localise to a limited set of languages as we need to have the capability internally to analyse the output.

As such, if you will look to add it the translation/source folder, it should preferably be in a new, separate file, where we can control the list of target languages it can be translated to.
For reference, you can set target languages on Crowdin via Sources > (on file) ... > Settings.

Alternatively, I'm very happy to upload a file to Crowdin so we keep it outside of source control. I would prefer to write a more tailored, one-off message in this instance, so would please like your steer as to how this should be approached.

[ornicar]

Because it's a one-off thing, I think we should keep its translation outside of the usual loop.

Add the translations here when you're satisfied with them, and I'll hardcode them into the survey sender script.