Speed up the IBD by increasing dbcache

[epiccurious]

Check if the user's system will support in increased dbcache

The risk of increasing dbcache too much is creating system instability and rolling blocks, so need to understand this issue better before making a change.

For example, if a user's system has 16GB and there are 6GB of RAM free, setting dbcache to 2 GB shouldn't be a problem. But if the user's system has 16GB and there are 2 GB free, setting dbcache to 2 GB will cause problems.

[epiccurious]

Adding UI/UX tag because modifying RAM usage to speed up IBD affects the UX.

[epiccurious]

Here's how to see how much memory the system has in total and currently available:
grep -E "MemTotal|MemAvailable" /proc/meminfo

[epiccurious]

This issue will not be part of the Minimum Viable Product milestone.