meta/sql: more connection control options

[anysql]

Add four new options for sql meta engine

1, max-open-conns, limit the maximum connection, default 0 (unlimited)
2, max-idle-conns, limit the maximum idle connection, previous is cpu number * 2, the new default is 10
3, max-idle-time, previous is 5 mins, no changed, just expose the option.
4, max-life-time, if a connection has be created more than given time, it will be closed anyway, default is 3600, as a backend connection may have some unclean resources.

[jiefenghuang]

Redis and KV have similar configurations, perhaps can change to a handling method similar to redis.ParseURL

[anysql]

Redis and KV have similar configurations, perhaps can change to a handling method similar to redis.ParseURL

Got.

[anysql]

Redis connection pool is provided by the driver, you can control the settings by meta url, we just need to make it clear in docuemnt.

While sql's connection pool is provided by the database/sql module, not by driver.

for redis/tikv: https://github.com/redis/go-redis/blob/91dddc2e1108c779e8c5b85fd667029873c95172/options.go#L451 setupConnParams function

[zhijian-pro]

These parameters are not universal, so it is more appropriate to use query parameters in the meta-url, which may be supported natively by the driver library.

[codecov]

Codecov Report

Attention: Patch coverage is 48.14815% with 28 lines in your changes missing coverage. Please review.

Project coverage is 54.92%. Comparing base (beaa0d0) to head (8794f76).
Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/meta/sql.go	48.14%	20 Missing and 8 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5512      +/-   ##
==========================================
- Coverage   55.09%   54.92%   -0.17%     
==========================================
  Files         166      165       -1     
  Lines       47787    47929     +142     
==========================================
  Hits        26327    26327              
- Misses      18613    18732     +119     
- Partials     2847     2870      +23     

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[anysql]

A better default setting may be "max_open_conns=30&max_idle_conns=30&max_idle_time=300&max_life_time=3600".

Let the max_idle_conns >= max_open_conns can eliminate the short connections effectively