PIN protection improvements: Longer timeout, manual locking, adaptive notification content

#### Is your feature request related to a problem? Please describe.

Currently when you set PIN protection for the app, you can choose to either require a PIN every time you open the app or after only 2 minutes (which is a relatively short period) of not using Element.

This does not allow for manual control of when to lock the app. The only way to 'manually' lock and unlock the app is to add a PIN when you need to lock it and remove the PIN when you don't want it to lock, rather than setting a PIN once and hitting lock/unlock as needed.

This is not very convenient, because sometimes you want the app to stay unlocked (when you're in a private and secure location or situation, i.e. at home) for ease of seeing messages and responding, and only lock it in certain situations such as in public or when you have to hand your phone over to someone else (and do not want them to see your messages).

#### Describe the solution you'd like.

Once you enable PIN protection, in addition to the automatic locking options, **add an option to keep the app unlocked unless locked by the user**.

Locking can be done and would be possible through either (both) of the following methods:

* In the app, tap on the three-dot menu in the top right corner and hit 'Lock'
* Outside the app, long press on the app icon and choose 'Lock'

#### Describe alternatives you've considered.

N/A

#### Additional context

Password managers (such as Bitwarden) emulate this behaviour by providing manual locking options in addition to automatic locking (through vault timeout).

More information [here](https://github.com/vector-im/element-android/issues/3108#issuecomment-814935101).