Reduce app size

#### Is your feature request related to a problem? Please describe.
Half of my friends don't have phones with lots of storage space, so most of the time they have to delete something else to be able to even install Element, or they just run out of space after using it for a while when combined with the storage used by the cache.

#### Describe the solution you'd like.
Look into reducing the app size of Element. I understand that that isn't as easy to control as it seems but it's a real problem to many people where I live where good phones aren't as affordable. I can't just ask my friends to get a better phone or delete files, when the apps they already use for communication use a lot less storage than Element. I'd appreciate any kind of optimization to reduce the app size, if possible.

#### Describe alternatives you've considered.
Limiting the cache usage. I think #3045 is related to that.

#### Additional context
My installation of Element is 119 MB in app size, which with the cache and user data adds up to 938 MB of internal storage usage.
Comparing it to WhatsApp, where the app size is just 63 MB (for me at least) and the max usage of chats (cache) has been like 300 MB at worst, it's a huge difference.

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Thank you for the work on Element Android <3