Added new memory visualization to DB Overview dashboard

[AlexeyBest]

Added new visualization to DB Overview dashboard: Memory by activities and instances.

This visualization is very helpful in OOM cases or when queries consume more memory than we expect.

• We can analyze which YDB component consumed memory.
• We can analyze how memory consumption was split between different hosts.

Changelog category

• Improvement

[github-actions]

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The tests on this PR will run after a maintainer adds an ok-to-test label to this PR manually. Thank you for your patience!

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• Additional args: custom ya make arguments

[github-actions]

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