Install: Fix directory path for prometheus install.sh

[Tomcli]

Why are these changes needed?

Right now the /install/prometheus/install.sh script is assuming the directory path is /install/prometheus/. However, the main README instruction is asking users to run this script from the top directory which will result the following errors:

+ monitor_dir=../../config/prometheus
+ pushd ../../config/prometheus
./install/prometheus/install.sh: line 14: pushd: ../../config/prometheus: No such file or directory

Therefore, we need to make sure monitor_dir is set to the right directory without depending on the user's current directory path.

Related issue number

None

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(

[Jeffwan]

This is a nice catch and thanks for the fix. Prometheus support is recently added and community may not have enough testing on user guide. Really appreciate your findings!