feat: replace mpstat with reading /prc/stat

[TetsuKawa]

Description

This PR changes following:

• replaces mpstat command with reading /proc/stat for performance.
• Treads that publish /diagnostics and reading cpu information are separated.

Related links

Tests performed

Confirmed that memory information is almost same as mpstat command.
Confirmed that publish /diagnostics at 1 Hz even when reading some information is timed out.
(This is confirmed by inserting sleep() in function reading some information.)

Confirmed that cpu usage information is almost same as mpstat command.
TODO: exception handling, performance

Notes for reviewers

Interface changes

Effects on system behavior

If it takes long time to read some cpu information, /diagnotics is not the most up-to-date information.
In the case, timeout can be determined only after reading process is completed.

Pre-review checklist for the PR author

The PR author must check the checkboxes below when creating the PR.

• I've confirmed the contribution guidelines.
• The PR follows the pull request guidelines.

In-review checklist for the PR reviewers

The PR reviewers must check the checkboxes below before approval.

• The PR follows the pull request guidelines.
• The PR has been properly tested.
• The PR has been reviewed by the code owners.

Post-review checklist for the PR author

The PR author must check the checkboxes below before merging.

• There are no open discussions or they are tracked via tickets.
• The PR is ready for merge.

After all checkboxes are checked, anyone who has write access can merge the PR.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity.

[mitsudome-r]

@TetsuKawa @ito-san Do you still need this modification?

[TetsuKawa]

@mitsudome-r
This is deprecated change.
Thank you for your announcement！