[Enhancement] Add datacache memory tracker to trace the datacache memory usage.

[GavinMar]

Why I'm doing:
The datacache memory usage is unobservable, which brings difficulties to analyze process memory details.

What I'm doing:
Add datacache memory tracker to trace the datacache memory usage.
You can observe the datacache memory usage by follow urls:

http://${BE_HOST}:${BE_WEBSERVER_PORT}/mem_tracker
http://${BE_HOST}:${BE_WEBSERVER_PORT}/metrics
http://${BE_HOST}:${BE_WEBSERVER_PORT}/metrics/memory

What type of PR is this:

• BugFix
• Feature
• Enhancement
• Refactor
• UT
• Doc
• Tool

Does this PR entail a change in behavior?

• Yes, this PR will result in a change in behavior.
• No, this PR will not result in a change in behavior.

If yes, please specify the type of change:

• Interface/UI changes: syntax, type conversion, expression evaluation, display information
• Parameter changes: default values, similar parameters but with different default values
• Policy changes: use new policy to replace old one, functionality automatically enabled
• Feature removed
• Miscellaneous: upgrade & downgrade compatibility, etc.

Checklist:

• I have added test cases for my bug fix or my new feature
• This pr needs user documentation (for new or modified features or behaviors)
  • I have added documentation for my new feature or new function
• This is a backport pr

Bugfix cherry-pick branch check:

• I have checked the version labels which the pr will be auto-backported to the target branch
  • 3.2
  • 3.1
  • 3.0
  • 2.5

[starrocks-cr]

The most risky bug in this code is:
Potential null pointer dereference.

You can modify the code like this:

// ...
BlockCache* block_cache = BlockCache::instance();
if (block_cache && block_cache->is_initialized()) { // Check if block_cache is not nullptr before using it
    auto datacache_metrics = block_cache->cache_metrics();
    datacache_mem_bytes = datacache_metrics.mem_used_bytes + datacache_metrics.meta_used_bytes;
}
// ...

Explanation:
In the code provided, there's a check for block_cache->is_initialized() but no check to ensure that block_cache is not a nullptr before calling is_initialized() on it. If BlockCache::instance() returns a nullptr, attempting to call is_initialized() or any other method on it will lead to undefined behavior and possibly crash the program. Therefore, it's important to add a null pointer check before using block_cache.

[github-actions]

[FE Incremental Coverage Report]

✅ pass : 0 / 0 (0%)

[github-actions]

[BE Incremental Coverage Report]

❌ fail : 2 / 14 (14.29%)

file detail

	path	covered_line	new_line	coverage	not_covered_line_detail
🔵	src/http/default_path_handlers.cpp	0	2	00.00%	[159, 160]
🔵	src/script/script.cpp	0	1	00.00%	[224]
🔵	src/common/daemon.cpp	0	9	00.00%	[120, 180, 181, 182, 183, 184, 185, 192, 193]
🔵	src/block_cache/block_cache.cpp	1	1	100.00%	[]
🔵	src/runtime/exec_env.cpp	1	1	100.00%	[]

[github-actions]

@Mergifyio backport branch-3.2

[github-actions]

@Mergifyio backport branch-3.1

[mergify]

backport branch-3.2

✅ Backports have been created

• #39524 [Enhancement] Add datacache memory tracker to trace the datacache memory usage. (backport #38884) has been created for branch branch-3.2

[mergify]

backport branch-3.1

✅ Backports have been created

• #39525 [Enhancement] Add datacache memory tracker to trace the datacache memory usage. (backport #38884) has been created for branch branch-3.1 but encountered conflicts