feat(envrc): add --accept-flake-config flag to templates

Overview

[x] I have tested the relevant changes locally.
[x] I have checked that nix flake check --impure passes.
[x] I have ensured my commits follow the project's conventional commits guidelines.
[x] I have checked that the changes follow a linear history.
[ ] (If applicable) I have commented any relevant parts of my code.
[ ] (If applicable) I have added appropriate unit/feature tests.
[ ] (If applicable) I have updated the documentation accordingly (in English).