Save run metadata in better format

[dachengx]

What is the problem / what does the code in this PR do

Just save run metadata in a format where indent is 4.

Can you briefly describe how it works?

Can you give a minimal working example (or illustrate with a figure)?

Please include the following if applicable:

• Update the docstring(s)
• Update the documentation
• Tests to check the (new) code is working as desired.
• Does it solve one of the open issues on github?

Please make sure that all automated tests have passed before asking for a review (you can save the PR as a draft otherwise).

[github-actions]

coverage: 90.401% (-0.03%) from 90.428%
when pulling d07e58b on better_write_run_metadata
into a58cd5d on master.

[coveralls]

coverage: 90.445% (+0.02%) from 90.428%
when pulling d07e58b on better_write_run_metadata
into a58cd5d on master.