SSH agent keys get removed even when other databases are closed

[snstamml]

Expected Behavior

SSH agent keys from databases B, C, D... should not be removed from the key agent when database A is closed. Only keys from database A should be removed.

Current Behavior

When closing database A, SSH agent keys from database B (or any other database) registered with the key agent are removed.

Possible Solution

Check from which database an agent key derives from, and remove only those that come from the database that is being closed.

Steps to Reproduce

1. Create and open databases A and B
2. Create an entry in database B with a "SSH Agent" key and click "Add to agent"
3. Check the key list in the SSH agent (e.g. Pageant on Windows)
4. Close database A
5. Check the key list in the SSH agent

Context

Every time any database is closed, all keys from the other databases need to be manually re-added to the key agent.

Debug Info

KeePassXC - Version 2.5.3
Revision: f8c962b

Qt 5.13.2
Debugging mode is disabled.

Operating system: Windows 10 (10.0)
CPU architecture: x86_64
Kernel: winnt 10.0.18363

Enabled extensions:

• Auto-Type
• Browser Integration
• SSH Agent
• KeeShare (signed and unsigned sharing)
• YubiKey

Cryptographic libraries:
libgcrypt 1.8.5

[hifi]

We don't currently track the database a key was added from which causes this issue.

It either needs to be "hacked" in as an extra argument to SSHAgent::addIdentity or a more creative solution be figured out. I don't like changing the API just to have an extra argument for this purpose but it may be an interim solution.

Whatever the final solution is the corner case of not having a database when adding a key (however unlikely) needs to be accounted for.

[droidmonkey]

Recommend tying it to the Database UUID.