CMSSW Micro-Architecture Support for x86_64

Starting from CMSSW_14_0_X, releases are built with support for multiple micro-architectures on x86_64.

For CMSSW_14_X:

The default micro-architecture is x86-64-v2.
An additional micro-architecture, x86-64-v3, is also available.
To optimize time and resource usage, SCRAM is configured by default to use only x86-64-v2.
If you need x86-64-v3 libraries and plugins in CMSSW, run:
```
scram build enable-multi-targets
```
in your development area. This enables SCRAM to build your checked-out packages for both micro-architectures and automatically select the best set of libraries at runtime.

For CMSSW_15_0_X and Later: Starting with CMSSW_15_0_X, the following changes apply:

Default Micro-Architecture: x86-64-v3
Additional Micro-Architecture: x86-64-v2
Runtime Environment Selection (cmsenv):
- Nodes with only x86-64-v2 support: The runtime environment will use x86-64-v2 libraries and plugins.
- Nodes with x86-64-v3 (or higher) support: The runtime environment will use x86-64-v3 libraries and plugins.
Development Area Configuration:
- Nodes with only x86-64-v2 support: SCRAM will enable multi-microarchitecture support. Checked-out packages will be built for both x86-64-v2 and x86-64-v3, with SCRAM selecting the best match at runtime.
- Nodes with x86-64-v3 (or higher) support: SCRAM will disable multi-microarchitecture support. Checked-out packages will be built only for x86-64-v3, and at runtime, SCRAM will use only x86-64-v3 libraries.
New Environment Variables Set by SCRAM (for CMSSW_15_0_X and later):
- SCRAM_DEFAULT_MICROARCH: Specifies the default micro-architecture for the CMSSW release (e.g., x86-64-v3 for CMSSW_15_0_X).
- SCRAM_MIN_SUPPORTED_MICROARCH: Defines the minimum required micro-architecture for CMSSW.
  - If multi-microarchitecture support is enabled in the development area, this will be set to x86-64-v2.
  - Otherwise, it will be set to x86-64-v3