issue-1751: [Filestore] WriteBackCache: Extend metrics

[e673]

Notes

Describe your PR - what it does and why this needs to be done.

Issue

Put links to the related issues here

[github-actions]

Note

This is an automated comment that will be appended during run.

🟢 linux-x86_64-relwithdebinfo target: cloud/tasks/,cloud/storage/ (test time: 244s): all tests PASSED for commit 8e8c45f.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
864	864	0	0	0	0	0

🟢 linux-x86_64-relwithdebinfo target: cloud/disk_manager/ (test time: 219s): all tests PASSED for commit 8e8c45f.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
1091	1091	0	0	0	0	0

🔴 linux-x86_64-relwithdebinfo target: cloud/blockstore/ (test time: 1464s): some tests FAILED for commit 8e8c45f.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
5958	5953	0	4	0	1	0

🟢 linux-x86_64-relwithdebinfo target: cloud/blockstore/ (test time: 43s): all tests PASSED for commit 8e8c45f.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
66	66	0	0	0	0	0

🟢 linux-x86_64-relwithdebinfo target: cloud/filestore/ (test time: 5292s): all tests PASSED for commit 8e8c45f.

TESTS	PASSED	ERRORS	FAILED	FAILED BUILD	SKIPPED	MUTED?
3523	3523	0	0	0	0	0