docs(glue-alpha): fix inconsistent structures in README (#35340)

### Reason for this change



There are inconsistencies in the README structure. Fixed them into unified structure. 

### Description of changes



- I made Spark Jobs as subheader as they provide examples and core part of L2 construct. I kept triggers as numbered list as they do not provide any examples and no need to highlight them. 


### Checklist
- [X] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: ozelalisen

packages/@aws-cdk/aws-glue-alpha/README.md

@@ -68,7 +68,7 @@ for more granular details.
 
 ### Spark Jobs
 
-1. **ETL Jobs**
+#### ETL Jobs
 
 ETL jobs support pySpark and Scala languages, for which there are separate but
 similar constructors. ETL jobs default to the G2 worker type, but you can
@@ -130,7 +130,7 @@ new glue.PySparkEtlJob(stack, 'PySparkETLJob', {
 });
 ```
 
-**Streaming Jobs**
+#### Streaming Jobs
 
 Streaming jobs are similar to ETL jobs, except that they perform ETL on data
 streams using the Apache Spark Structured Streaming framework. Some Spark
@@ -186,7 +186,7 @@ new glue.PySparkStreamingJob(stack, 'PySparkStreamingJob', {
 });
 ```
 
-**Flex Jobs**
+#### Flex Jobs
 
 The flexible execution class is appropriate for non-urgent jobs such as
 pre-production jobs, testing, and one-time data loads. Flexible jobs default
@@ -419,14 +419,14 @@ override it if you prefer for your trigger not to start on creation.
 Reference the workflow-triggers.test.ts unit tests for examples of creating
 workflows and triggers.
 
-1. **On-Demand Triggers**
+#### **1. On-Demand Triggers**
 
 On-demand triggers can start glue jobs or crawlers. This construct provides
 convenience functions to create on-demand crawler or job triggers. The constructor
 takes an optional description parameter, but abstracts the requirement of an
 actions list using the job or crawler objects using conditional types.
 
-1. **Scheduled Triggers**
+#### **2. Scheduled Triggers**
 
 You can create scheduled triggers using cron expressions. This construct
 provides daily, weekly, and monthly convenience functions,
@@ -454,13 +454,13 @@ The trigger actions are executed when the predicateCondition is true.
 A `Connection` allows Glue jobs, crawlers and development endpoints to access
 certain types of data stores.
 
-***Secrets Management
-    **You must specify JDBC connection credentials in Secrets Manager and
+* **Secrets Management**
+    You must specify JDBC connection credentials in Secrets Manager and
     provide the Secrets Manager Key name as a property to the job connection.
 
 * **Networking - the CDK determines the best fit subnet for Glue connection
-configuration
-    **The prior version of the glue-alpha-module requires the developer to
+configuration**
+    The prior version of the glue-alpha-module requires the developer to
     specify the subnet of the Connection when it’s defined. Now, you can still
     specify the specific subnet you want to use, but are no longer required
     to. You are only required to provide a VPC and either a public or private