Added matrix-media-repo role

Making the group match the Ansible task tags allows people to do `just install-service matrix-media-repo` and have that trigger both `--tags=matrix-media-repo` and also restart just that single group (`matrix-media-repo`).

Update mautrix-discord 0.5.0 -> 0.6.0

Upgrade sliding-sync (v0.99.3 -> v0.99.4)

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

Explain the option of manually defining your public IP in the documentation for Coturn

Explicitly refer users to the relevant roles file so people know where to find the additional configuration options.

I was very surprised by the fact that a rather important configuration for coturn was "hidden" in the Hosts file, but not mentioned here. 

Therefore my suggestion is to explicitly mention it here, as I believe that is that natural for people to look.

Bump ansible-community/ansible-lint-action from 6.16.0 to 6.17.0

Bumps [ansible-community/ansible-lint-action](https://github.com/ansible-community/ansible-lint-action) from 6.16.0 to 6.17.0.
- [Release notes](https://github.com/ansible-community/ansible-lint-action/releases)
- [Commits](https://github.com/ansible-community/ansible-lint-action/compare/v6.16.0...v6.17.0)

---
updated-dependencies:
- dependency-name: ansible-community/ansible-lint-action
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Related to:
- e4f545c452
- 2481b7dfa4

We've prepared for this by adding the `main` process to the `instance_map` a long time ago,
in 49cb8b7b11.

Upgrade sliding-sync (v0.99.1 -> v0.99.3)

Related to 0f02f0b4da

fix(linkedin): mismatched appservice id

Updated to match value in
`roles/custom/matrix-bridge-beeper-linkedin/templates/config.yaml.j2`.

Add note for -K flag to Ansible