dashboard: add panels for transaction operations

[DifferentialOrange]

Add panels for transaction operations (begin, commit, rollback). Metrics were introduced in 2.10.0-beta1 [1] and fixed in 2.10.4 and 2.11 [2].

1. tarantool/tarantool@48c8dc1
2. tarantool/tarantool@a5fe5c3

Closes #176

If this pull request introduces support for new metrics, do not forget to

• add Grafana panel;
• run make update-tests to build new dashboard artifacts;
• add example application code to generate non-null metrics;
• attach a screenshot of a new panel to the PR description;
• add new Telegraf tag key, if relevant,
  • to all telegraf.conf files,
  • to "Grafana dashboard" documentation page;
• add alert example, if relevant,
  • to alerts.yml,
  • to "Alerting" documentation page;
• update supported_metrics.md.

In any case, do not forget to

• link an issue;
• add a CHANGELOG entry;
• update documentation guidelines;
• update README guidelines.