Merged PR 278: Enable the red agent to vary its start node

## Summary
- Made the data manipulation red agent be able to choose between the two clients to start operating on
- changed the attacker name in the config to 'data_manipulation_attacker' to because it is no longer tied to any client
- Updated the documentation notebook accordingly.
- Fixed a bug where the database client made a new connection every time it sent a SQL query (it tries to reuse its most recent one instead)
- Fixed a bug where link loads were not being cleared between episodes (?)

**warning** - the green agents are not working properly after reset right now, but I'm gonna fix this in the next ticket where I refactor episode reset.

## Test process
- unit tests pass
- UC2 notebook passes with both clients. (currently this doesn't work after an episode reset, but the very next thing I'm gonna work on is refactoring the reset, so I don't want to waste time fixing this.)

## Checklist
- [x] PR is linked to a **work item**
- [x] **acceptance criteria** of linked ticket are met
- [x] performed **self-review** of the code
- [x] written **tests** for any new functionality added with this PR
- [ ] updated the **documentation** if this PR changes or adds functionality
- [ ] written/updated **design docs** if this PR implements new functionality
- [x] updated the **change log**
- [x] ran **pre-commit** checks for code style
- [n] attended to any **TO-DOs** left in the code

Related work items: #2232

CHANGELOG.md

@@ -6,6 +6,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+- Changed the red agent in the data manipulation scenario to randomly choose client 1 or client 2 to start its attack.
 - Changed the data manipulation scenario to include a second green agent on client 1.
 - Refactored actions and observations to be configurable via object name, instead of UUID.
 - Fixed a bug where ACL rules were not resetting on episode reset.