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[bot]]

Hi! Thank you for contributing! 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!

[ydbot]

Run Extra Tests

Run additional tests for this PR. You can customize:

• Test Size: small, medium, large (default: all)
• Test Targets: any directory path (default: ydb/)
• Sanitizers: ASAN, MSAN, TSAN
• Coredumps: enable for debugging (default: off)
• Additional args: custom ya make arguments

[github-actions[bot]]

:red_circle: 2025-12-12 08:23:57 UTC The validation of the Pull Request description has failed. Please update the description.

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