Allow defining shared memory size at runtime

[NobinPegasus]

Description

I have declared extern size_t BPFTIME_SHARED_MEMORY_SIZE; inside bpftime_shm_internal.hpp and inside bpftime_shm_internal.cpp defined the size_t BPFTIME_SHARED_MEMORY_SIZE = 20; // Default size

Then inside the cli/main.cpp I have added support for --shared-memory-size.

Fixes #282

Type of change

• Bug fix (non-breaking change which fixes an issue)
• [✅] New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Test A
• Test B

Test Configuration:

Checklist

• [✅] My code follows the style guidelines of this project
• [✅] I have performed a self-review of my own code
• [✅] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• [✅] I have checked my code and corrected any misspellings

[Officeyutong]

@NobinPegasus Is this PR finished yet? I haven't seen things related to read environment variables

[NobinPegasus]

@Officeyutong I've make changes in tools/cli/main.cpp. Can you check it? And provide feedback?

[yunwei37]

What I have done is:

1. Add new env var for shm size
2. Make the config a separate file
3. Fix the wrong default value of the config

The document also needs to be changed, since we set the JIT as default engine.

Another thing I need to do in the next PR is

• merge the syscall server config with this config
• rename agent config to bpftime_config, so it's global

[Officeyutong]

Will bytes be better?

[Officeyutong]

Comment should be updated