Add "Features" section to READMEs

[hknutsen]

Add a "Features" section to module repo READMEs (just under the introduction) where we can list notable features for the modules.

• docs: add features section to README terraform-azurerm-web-app#198
• docs: add features section to README terraform-azurerm-sql#150
• equinor/postgres/azurerm
• docs: add features section in README terraform-azurerm-function-app#70
• docs: add features list to README terraform-azurerm-service-bus#59
• equinor/identity/azurerm
• chore: update variable descriptions and add features list terraform-azurerm-app-config#33
• equinor/event-grid/azurerm
• docs: add "Features" section to README terraform-azurerm-key-vault#94
• chore: update variable descriptions and add features list terraform-azurerm-automation#53
• equinor/public-ip/azurerm
• chore: update variable descriptions and add features list terraform-azurerm-acr#75
• equinor/nat/azurerm
• equinor/container-app/azurerm
• chore: update variable descriptions and add features list terraform-azurerm-app-service#18
• docs: add features list to README terraform-azurerm-vm#52
• docs: update variable descriptions and add features list terraform-azurerm-grafana#37
• docs: add features list to README terraform-azurerm-app-insights#48
• equinor/synapse/azurerm
• chore: update variable descriptions and add features list terraform-azurerm-databricks#40
• docs: add features list to README terraform-azurerm-network#75
• docs: add features section to README terraform-azurerm-storage#228
• docs: add features list to README terraform-azurerm-log-analytics#55
• https://github.com/equinor/terraform-module-template
• Add best practice to keep features section up-to-date as notable features get added

[helenakallekleiv]

List of modules with updated READMEs:

• docs: add "Features" section to README terraform-azurerm-key-vault#94

[hknutsen]

Putting on hold until anyone picks this up and actively works on it again.