Correct broken documentation link

Recently, documentation on Synapse has been changed from .rst to .md. Therefore, the current links for the purge history API were resulting in a 404 error.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1154

According to
https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Content-Security-Policy,
having both a header and the `<meta>`-tag provided by Element itself is
not a problem. The 2 CSP policies get combined.

Updating to latest synapse release (performance regression)

https://github.com/matrix-org/synapse/releases/tag/v1.37.1

postgres minor updates

Update IRC bridge

heisenbridge: fix service name in setup_uninstall.yml

Remove asterisks from configuring-dns.md

These previously denoted optional DNS records but now optional records are a separate table so they are unnecessary.

Update hydrogen main.yml

update to v0.2.0

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1140

Update prometheus  v2.27.1 -> v2.28.0

Coturn update 4.5.2 -> 4.5.2-r2

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1131

The new one is based on Alpine 3.14, instead of Alpine 3.13.

Add support for CentOS (Stream) 8

according to discussion in channel not needed anymore

Content-Security-Policy For Element Web

Update grafana 8.0.2 -> 8.0.3

https://github.com/vector-im/element-web#configuration-best-practices

Should have been part of 9daeb39710

Update configuring-playbook-synapse.md

Added an example for configuring the variables for the OpenID, that might fails because the variables are not defined for the playbook parsing, but Synapse's own config file parsing.

GoMatrixHosting v0.5.0

update hydrogen v0.1.56 -> v0.1.57

Update grafana 8.0.0 -> 8.0.2

https://github.com/vector-im/hydrogen-web/releases/tag/v0.1.57