[Bug] BossBar support in BungeeCord doesn't work in 1.20-R0.2-newer versions

[bivashy]

Describe the bug
BossBar doesn't appear in new BungeeCord versions (1.20-R0.2 and newer), probably because BossBar was moved into another module, which leads into incompatibility, probably we should consider using Adventure API for broadcasting BossBar to players, instead of relying into legacy/unreliable native implementation of BossBar.

To Reproduce
Steps to reproduce the behavior:

1. Download latest version of BungeeCord
2. Enable bossbar in configuration
3. See that bossbar doesn't appear at all

Expected behavior
BossBar should appear as usual.

Screenshots
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Additional context
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[bivashy]

#155