Update encryption algorithms in Flume appender

## Description

The Flume appender uses:
```java
Cipher.getInstance("AES");
```
to encrypt messages

In the default [Oracle security providers](https://docs.oracle.com/en/java/javase/17/security/oracle-providers.html#GUID-BC92B7F1-D15C-432A-B725-9BBA9FEF61DB) this uses `ECB` as cipher mode, which:

- does not provide integrity (cf. [CIPHER_INTEGRITY](https://find-sec-bugs.github.io/bugs.htm#CIPHER_INTEGRITY)),
- does not provide good confidentiality (cf. [ECB_MODE](https://find-sec-bugs.github.io/bugs.htm#ECB_MODE)).

If Flume supports it, we should replace it with another cipher mode.

Related to #1707.