☂ Cherry-pick next hop selection PR suite to v9.0.x

[zwoop]

Creating this issue to track all the dependencies etc. for this feature.

• Add Nexthop selection strategies and @strategy tag to remap.config. #5960 - Add Nexthop selection strategies and @strategy tag to remap.config.
• Fix the strategies.yaml documentation. #6206 - Fix the strategies.yaml documentation.
• Fixes spelling in strategies.yaml docs #6208 - Fixes spelling in strategies.yaml docs
• Cleanup trailing whitespaces, and YAML formatting #6210 - Cleanup trailing whitespaces, and YAML formatting
• This fixes next hop unit tests that segfault due to missing unit test yaml files. #6216 - This fixes next hop unit tests that segfault due to missing unit test yaml files.
• Fixed next hop tests for out of tree builds #6219 - Fixed next hop tests for out of tree builds
• Adds strategies.yaml to install target #6240 - Adds strategies.yaml to install target
• Fixes sphinx build warning with the strategies.yaml document in the admin-guide #6242 - Fixes sphinx build warning with the strategies.yaml document in the admin-guide
• LGTM: fix a comparison that is always false. #6270 - LGTM: fix a comparison that is always false.
• Update the admin-guide hierachical caching and remap.config documentation. #6279 - Update the admin-guide hierachical caching and remap.config documentation.
• Fixes a case where the NextHop consistent hash ring may not be completely searched. #6303 - Fixes a case where the NextHop consistent hash ring may not be completely searched.
• Fixes an issue where NextHopSelectionStrategy did not implement a parent check. #6339 - Fixes an issue where NextHopSelectionStrategy did not implement a parent check.

[zwoop]

Blocks #5932

[zwoop]

All done.