Move templates to api directory

In order to access templates while running API from python
package, move `templates` to `api` directory.
Update `pyproject.toml` to include `api/templates` directory
to the python package.
Update `api.user_manager` to use `PackageLoader` to load
templates from the python package.

Signed-off-by: Jeny Sadadia <[email protected]>

Author: Jeny Sadadia

api/templates/email-verification-successful.jinja2

@@ -0,0 +1,8 @@
+{# SPDX-License-Identifier: LGPL-2.1-or-later -#}
+
+Hello {{ username }},
+
+Your email address has been verified successfully.
+
+Thanks,
+KernelCI SysAdmin

api/templates/email-verification.jinja2

@@ -0,0 +1,10 @@
+{# SPDX-License-Identifier: LGPL-2.1-or-later -#}
+
+Hello {{ username }},
+
+The token for verifying your email address for KernelCI API account is:
+
+  {{ token }}
+
+Thanks,
+KernelCI SysAdmin

api/templates/reset-password-successful.jinja2

@@ -0,0 +1,8 @@
+{# SPDX-License-Identifier: LGPL-2.1-or-later -#}
+
+Hello {{ username }},
+
+Your password reset is successful.
+
+Thanks,
+KernelCI SysAdmin

api/templates/reset-password.jinja2

@@ -0,0 +1,10 @@
+{# SPDX-License-Identifier: LGPL-2.1-or-later -#}
+
+Hello {{ username }},
+
+The token to reset your password for KernelCI API account is:
+
+  {{ token }}
+
+Thanks,
+KernelCI SysAdmin