General: Move formatting and workfile functions

[iLLiCiTiT]

Brief description

Move functions from avalon that are related to calculation of last workfile path and optional template formatting.

Description

Usage of format_template_with_optional_keys function is replaced with StringTemplate.
Functions last_workfile_with_version renamed to get_last_workfile_with_version and last_workfile renamed to get_last_workfile and both moved to openpype/lib/avalon_context.py.

Testing notes:

1. Workfiles tool should be able to find last workfile version and use next available (when save as is clicked)
2. Last workfile should be launched on host start (if the feature is enabled!)
3. Modified string formatting should work as did

Related to PR ynput/avalon-core#434

[ynbot]

Task linked: OP-2947 move formatting and workfile functions