Clear Atlas tech debt

[zabeen]

Note, the assumption is that none of these items will lead to breaking, API-level changes. If any do, then they need to added to a new card and marked with next milestone version: 3.0.0.

It is worth going through the tech-debt backlog to see if there is anything else worth prioritising.

Update Frameworks and Packages

• [x] #1285
• [x] #1305
• [x] #1159
• [x] #819
• [x] Refactoring of Dependency Injection for client (introduce the keyed registration)
• [ ] #1052
• [ ] Update other outdated/deprecated packages

Build Warnings

Some of the existing warnings maybe resolved by updating packages.

• [ ] Remove non-API level code that was marked obsolete in previous Atlas versions (API-level code should be removed under a 3.0.0 ticket)
• [ ] #1071
• [ ] Clear remaining build warnings

[SergeyEzh]

@daria-sorokina-da, @zabeen , It seems that #1159 requires migration function apps from in-process model to isolated worker.