[ENH] Creating a new Bayesian Regressor with PyMC as a backend (#358)

#### Reference Issues/PRs
#7

#### What does this implement/fix? Explain your changes.
This PR implements a Bayesian Linear Regressor with PyMC as a
backend

#### Does your contribution introduce a new dependency? If yes, which
one?
Yes - it depends on PyMC family: PyMC itself, XArray and ArviZ

.all-contributorsrc

@@ -182,7 +182,9 @@
       "avatar_url": "https://avatars.githubusercontent.com/u/37468543?v=4",
       "profile": "https://github.com/meraldoantonio",
       "contributions": [
-        "bug"
+        "bug",
+        "code",
+        "doc"
       ]
     },
     {

pyproject.toml

@@ -57,6 +57,7 @@ all_extras = [
     "ngboost<0.6.0; python_version < '3.13'",
     "polars<1.14.0",
     "pyarrow<14.0.0; python_version < '3.12'",
+    "pymc; python_version < '3.13'",
     "scikit-survival<0.24.0; python_version < '3.13'",
     "statsmodels>=0.12.1",
 ]