Change the default working directory from `/tmp` to ...

[MichaelScofield]

What type of enhancement is this?

User experience

What does the enhancement do?

Currently the default working directory for GreptimeDB is /tmp/greptimedb, it's hardcoded in our codes, like here and here. That could cause problems for some impatient users who don't read our configuration document carefully enough:

• the /tmp does not exist in Windows OS;
• the contents in /tmp usually do not survive across system reboot;
• /tmp could be treated(mounted) differently than normal file system on disk, not good for getting consistent benchmarking results between users.

I think from perspective of user experience, we'd better change it from /tmp to some places on disk. The options I could think of are:

• $HOME/.greptimedb
• ./greptimedb

I'd prefer the first one.

Implementation challenges

Find a place to put the default working directory const in codes.