Move Commet defaults out of the Element section into a dedicated matrix-client-commet block, and add missing matrix_client_commet_enabled default wiring.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/5000

When no identity server is configured, `matrix_client_element_default_is_url`
defaults to `~` (YAML null). The `| string | to_json` filter chain converts
this to the literal string `"None"`, causing Element Web to log errors:

- TypeError: URL constructor: None is not a valid URL
- Invalid base_url for m.identity_server

The well-known template (`.well-known/matrix/client.j2`) already handles
this correctly with a conditional guard (see PR #314). This applies the
same pattern to the Element Web `config.json.j2` template.

OTW many empty dirs are kept

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

Signed-off-by: Suguru Hirahara <did🔑z6MkvVZk1A3KBApWJXv2Ju4H14ErDfRGxh8zxdXSZ4vACDg5>

This was causing issues when it's parsed out by certain tools.

Regression since 28afbde971

Co-authored-by: spantaleev <388669+spantaleev@users.noreply.github.com>

Co-authored-by: spantaleev <388669+spantaleev@users.noreply.github.com>

Co-authored-by: spantaleev <388669+spantaleev@users.noreply.github.com>

The companion role was tightly coupled to Synapse through shared tags, worker routing, and lifecycle ordering. Keeping them separate added coordination overhead without practical benefits, especially for parallelized execution.

This merges the role into matrix-synapse while keeping companion logic organized under dedicated reverse_proxy_companion task/template subdirectories.

Compatibility is preserved:
- matrix_synapse_reverse_proxy_companion_* variable names remain unchanged
- install/setup companion-specific tags remain available

Cross-role/global wiring is now in group_vars (matrix-synapse section), while role defaults provide sensible standalone defaults and self-wiring for Synapse-owned values.

Only queue matrix-goofys.service for restart when Synapse is enabled. Goofys is installed from the Synapse role, so non-Synapse homeserver configurations should not try to restart this unit. This mirrors the fix for issue https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4959.

Only queue matrix-synapse-s3-storage-provider-migrate.timer for restart when Synapse is actually enabled. This prevents setup/install failures when a Synapse-only extension flag is set while using another homeserver implementation, as reported in https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/4959.

With everything moving to Matrix RTC and Element X on mobile not
supporting legacy calls, most people probably don't need Coturn
auto-enabled.