[Bazel][1.x][Part 1]: Bazel + BazelToolchain refactor

[franramirez688]

Changelog: Feature: BazelToolchain creates a conan_bzl.rc file which defines the conan-config configuration. If it exists, Bazel helper will use it automatically.
Docs: conan-io/docs#3457
Closes: #14282 #14519

Next PR (BazelDeps): #14959

Overall, this PR is introducing no compatible changes, but deprecating some existing variables.

Summary:

• BazelToolchain is generating a conan_bzl.rc file with a build:conan-config configuration depending on your settings/options.
• BazelToolchain is not generating a real Bazel toolchain (https://bazel.build/extending/toolchains) because they require much more knowledge and expertise in Bazel to make a dynamic Bazel toolchain per user configuration.
• Bazel is moving forward to platforms (https://bazel.build/extending/platforms) for future releases instead of toolchains but it does not imply that BazelToolchain could be incompatible but some changes to inject those platforms constraints in our conan-config configuration.

[franramirez688]

@czoido seems that bazel is not installed in macOS machines 😢

The same test was already passing correctly for Conan 2.x (#14845)

UPDATED:
@czoido Tests passing, solved! 👏

[czoido]

I think there's a problem that we should resolve on how Bazel caches the artifacts and Conan packages it after the build.
The problem is that if for example, you create a bazel package and the library is packaged ok, because the artifacts are taken from the Bazel cache to the Conan cache, but then you make some modifications to the package, and change the name of the library for another one, then the old and new library are taken from the Bazel cache and two libs are packaged. To reproduce:

conan new mypackage/1.0 -m bazel_lib
conan create . -> libmypackage.a is stored in Conan cache
# replace name = "mypackage", in the BUILD file for name = "mypackagewithothername",
conan create . -> libmypackage.a and libmypackagewithothername.a are both stored in Conan cache

[franramirez688]

The next PR solves this issue. That one introduces changes in the template to let users create/consume shared libraries in all the platforms.

[memsharded]

Overall looking good, but my concerns about breaking too much, and I'd try to minimize it.

[czoido]

I think we can make here a explicit recomendation of setting self.folders.generators_folder = "conan" so that users can have a clue on what to do, but we can change that in the next PR