[connectors composer/manager] Prepare connectors for future migration

[Powlinett]

This PR aims to prepare codebase for future automated migration of all the connectors to be "manager supported" (i.e. enable deployment through OCTI UI).

The changes must concern only "not important things" such as encoding in docs/comments/logs, fix in sample files, update of dependencies versions... It must not change any connectors' behaviors.

Proposed changes

• replace characters to utf-8 equivalent (python files, READMEs, config files, etc)
  -> fix parsing errors during migration
• fix syntax errors in config.yml.sample files
  -> fix parsing errors during migration
• re-encode utf-16 encoded requirements.txt to utf-8
  -> fix parsing errors during migration
• update old versions of pycti in requirements.txt
  -> re-enable CI to update pycti versions during release
• move tests outside src directories
  -> avoid files mislocation during migration

Related issues

• [composer/catalog] Migrate connector to be connector manager supported - P1 #4857

Checklist

• I consider the submitted work as finished
• I have signed my commits using GPG key.
• I tested the code for its functionality using different use cases
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

Further comments

There's not much to test in this PR. If the CI passes and no change seems "dangerous", then it's ready for merge.