Add "My messages and context only" option to export (GDPR and single-chat)

[Niko-O]

Is your feature request related to a problem?

I am exporting all of my data from Telegram. I have selected as much data as possible (including private groups, and not only my messages) and as HTML and JSON. It's been 11 days since I started the export and the folder is over 200GB already, and it looks like it's only 20% done.

I took a quick look through the folder and most of the data comes from groups (which I assume are private) that are very active in general, but that I am very inactive in. So I don't care at all about 99% of the messages sent there.

This also applies to exporting messages from a single chat (i.e. three dots -> Export chat history)

Describe the solution you'd like

I would like to see an option to export only my own messages and the context around those messages.

• Any chains of replies to my messages should be included in the export.
• If my message was a reply to someone else's message, that other message should be included. And if that messsage was a reply to a message, that should be included, too.
• Often in a conversation, not everyone is replying to previous messages by explicitly making it a reply. Therefore, a few messages before and after my messages should be included, too. How many "a few" is, is up to debate. Ideally configurable in the export dialog. E.g. "Export N other user's messages before and after my own messages".
• A possible variation of the previous point would to be to go by time, e.g. "Export other user's messages that were posted N days/hours/minutes before and after my own messages."

Describe alternatives you've considered

For the GDPR export: Only exporting my own messages is not a valid solution because I want all messages (mine and others) for some groups.
For the single-chat export: Selecting a specific time-frame to export works in principle, but can become extremely cumbersome. Also see #5854

Additional context

No response